game programming workshop
TRANSCRIPT
BeginningGame Programming
Murray State UniversityComputer Science and Information Systems
Dr. Bob - [email protected]
This Workshop
The goal of this workshop is to give you a head start in beginning your study of game programming.
CD - Includes C/C++ compiler and code editor (IDE), Allegro 4.2 game development software library, tutorials and demo programs, other software tools useful for creating computer games.
Workshop covers:
Overview of Game Programming
How to Install C/C++ Compiler and Allegro
Using the Integrated Development Environment (IDE)
Running, reviewing, and modifying demo programs.
Game Programming as a Career
Computer game development is probably the most rapidly growing field in high technology today, but it is important to understand that you need to keep your options open.
"People looking at games courses… [should] consider what else you might be able to do if you can't get into the industry, where else you can go... somebody studying computer science, maths, or physics and then coming into a programming role, means that they can then go off into a number of different industries and be successful."
- Matthew Jeffrey (Head of Global Talent Brand at EA)
"Developers are considering applicants who have more general degrees (such as in computer science or fine art), even though these programs don't always give their students industry-specific training."
- Ben Kuchera (Opposable Thumbs journal)
"In my school, I had a game project with a random team. I did all the work while they played guitar hero and occasionally contributed barely-usable code (despite multiple efforts to engage them). I got a job and they did not. Could there be a correlation?!? I think there is! "
- Quasius
"I'm a programmer. I left the game industry and now I have better pay, much lower hours, and more flexibility (work from home, set my own hours). Now I actually have time to play games."
- nvanderh
“More and more companies are recruiting right from colleges. Regardless, of what college you go to, you can still get a job in the games industry provided you have a certain proficiency in the following areas.” Math, Physics, Extensive knowledge of C++, AI Programming, Graphics, Tools Development, Operating Systems, and Compilers."
- Matt Gilgenbach, a video game developer
Comments from Game Developers
Why Game Programming?
FORTUNE! GLORY! FUN!Programming games can be more fun than playing them.
Computer/Video Game Industry is now larger than the Movie Industry
A great new game can make its creator famous.
Game programming teaches many computer science (CS) topics:
Real-Time Systems Issues
Modeling/Physics
Graphics and Animation
Sound Generation
Graphical Design and Layout
Human/Computer Interfaces
Scientific Visualization
:
:
Types of Games
Classic Arcade
1st Person Shooter
RPG
Sports/Racing
Board Games
Adventure/Puzzle Solving
Flight Simulators
World Simulations
Strategy/Wargames
Fighting Games
Can One Person Still Write a Great Game ?
While many popular computer games are the result of 100s of programmers, designers, writers, artists, and producers, there is still a place for the lone programmer. The growing popularity of online (e.g. applet-level) games and games on PDA's, handhelds, and even cell-phones need great games. Lone programmers and small start-up game companies can fill this need.
YES!
Great Games come from Great Ideas
Each of the types of games started out as one game and one person's idea.
Establishing and Maintaining a Game Theme
One of the most important and most difficult parts of game design is a finding a good theme. The theme of a game affects the mood of the player. It is important to put some thought into choosing an good theme before jumping into the details of game design and development. Keep the theme of your game in mind as you design game objects, the background and characters, choose sounds, and decide on the order of the action.
The Game Loop
UpdateGame State
Get User Input
Sound
Graphics
Setup Game
done?
Stop Game
no
yes
wait
time through loop must be short and the
same for each pass
the amount of waitdepends on what else
has been done in this pass
Why Use Dev_C/C++ and Allegro
Open Source - That is to say, FREE!!!
Runs on PC's, or Mac's using most any Operating System:
Hugh Developer Network & Many User/Support Groups
http://alleg.sourceforge.net/wip.html
http://www.allegro.cc/
Large Number of Games and Software Tools Available
• Microsoft Windows • Linux• Mac OS X• Solaris• BeOS• FreeBSD
Enough Talk Already!Let's Get Started!!!
Installing Dev_C/C++
Open your Game Programming Workshop CD and copy the file named devcpp-4.9.9.2_setup.exe to your computer's desktop.
Run this install program. (Use the default values for all options.)
Find and open the Dev_Cpp folder on your computer (This folder should be installed at the root level, i.e. at C:\ )
Copy the folder named Test_Dev_Cpp from the CD into this folder.
Double click on the Dev-C++ desktop icon to launch the compiler.
Under File, choose Open Project or File..., and from inside the Dev-Cpp Test folder, select Test_Dev_Cpp.dev.
Under the Execute menu, select Compile and Run.
Loading the Allegro Software Library
Open the Allegro-minGW-4.2.0 folder on your CD.
Open the Dev_Cpp folder on your computer. Locate the folders named lib and include.
Copy the contents of the lib folder on the CD into the lib folder on your computer. (Note: Don't copy the folder, just its contents.
Copy the contents of the include folder on the CD (including the sub-folder named allegro) into the include folder on your computer.
Copy the contents of the bin folder on the CD into the C:\Windows\System32\ folder on your computer. (These are files with a .dll extension)
From your CD copy the folder named Test_Allegro into the Dev_Cpp folder on your computer.
From the File menu, choose Open Project or File... and select Test_Allegro.dev.
From the Execute menu, choose Compile and Run.
Wow! That was easy...Now we are ready to create our own projects.
1. Click on New Project taskbar icon.
2. Create an Empty Project named First_Project3. Create a new source file called main.cpp and add it to the current project.
Wow! That was easy...Now, we will learn how to create our own project...
4. Right-click First_Project and choose Project Options5. Under the General Tab select Win32 GUI Type
6. Under Parameters Tab add the line -lalleg to Linker and click on OK.
You are now ready to begin writing a graphics program.
#include <allegro.h>
int main(void)
{
allegro_init();
allegro_exit();
return 0;
}
END_OF_MAIN()
First_Project
// includes allegro library in project
// starts and ends allegro// graphics commands go between these lines
Enter this text in the editor, save, compile and run it.
Since there are no graphics commands, nothing will appear but you should get an error-free compile.
What Happened?If you typed everything correctly your program should have compiled and run with no messages and no display. Otherwise you will see error messages... The first error wll be
highlighted in the text with a message trying to tell you what when wrong.
Fix each error in the order they appear and only one at a time. This is because the error checker is a dumb program that can get lost.
This problem is so common it has a special name:
ERROR PROPAGATION
#include <allegro.h>
int main(void)
{
allegro_init();
set_gfx_mode(GFX_SAFE, 640, 480, 0, 0);
install_keyboard();
while(!key[KEY_ESC]);
allegro_exit();
return 0;
}
END_OF_MAIN()
First_Project
Now add these lines between allegro_init() and allegro_exit(): set_gfx_mode( ) defines a display 640 x 480 pixels install_keyboard( ) lets your program take command from the keyboard while(!key[KEY_ESC]) tells the program to wait on this line until the ESC key has been pressed
#include <allegro.h>
int main(void)
{
allegro_init();
set_gfx_mode(GFX_SAFE, 640, 480, 0, 0);
install_keyboard();
while(!key[KEY_ESC]);
allegro_exit();
return 0;
}
END_OF_MAIN()
First_Project
When we run the program this time, a rectangular display window named First_Project should appear with a black background. This is the window that will display the graphics, when we tell the program what to display.
Allegro gives this window the name, screen.
The whle( ) statement tells the program to wait until the user presses the ESC key.
Drawing in the Graphics Window
#include <allegro.h>
#define BLUE makecol(0,0,255)
int main(void)
{
allegro_init();
set_gfx_mode(GFX_SAFE, 640, 480, 0, 0);
install_keyboard();
rect(screen,50,60,150,160,BLUE);
while(!key[KEY_ESC]);
allegro_exit();
return 0;
}
END_OF_MAIN()
defines the color BLUE using red, green, blue (RGB) values
this statement tells the program to draw a rectanglein the graphics window withone corner at x=50, y=60 andthe opposite corner at x=150and y=160 (100x100 pixel box)
A Closer Look
640
480
0,0
each point in this window is defined by a pair of numbers (x,y)
640,0
50,60
150,160
incr
easi
ng y
increasing x
rect(screen,50,60,150,160,BLUE)
RGB Color Values
Each value is a number between 0 and 255.
Mixing Light is additiveso 255,255,255 makeswhite
255,0,0
255,0,255
255,255,0
0,255,0
0,0,255
0,255,255
0,0,0 = BLACK makecol(rval,gval,bval) can beused to create over 16 millioncolors
Try These Drawing Commands
int my_color;
my_color = makecol(255,255,0);
putpixel(screen,320,240,my_color);
line(screen,10,100,630,100,my_color);
rectfill(screen,200,300,250,370,makecol(100,0,200));
circle(screen,230,110,30,makecol(50,200,10));
circlefill(screen,500,400,10,makecol(0,0,100));
ellipsefill(screen,185,210,100,30,makecol(50,50,50));
ellipsefill(screen, 180,200,100,30,makecol(255,0,0));
ellipse(screen, 175,195,100,30,makecol(255,180,180));
Example Shapes
putpixel(screen,320,240,my_color);
line(screen,10,100,630,100,my_color);
rectfill(screen,200,300,250,370,makecol(100,0,200));
circle(screen,230,110,30,makecol(50,200,10));
circlefill(screen,500,400,10,makecol(0,0,100));
ellipsefill(screen,185,210,100,30,makecol(50,50,50));ellipsefill(screen, 180,200,100,30,makecol(255,0,0)); ellipse(screen, 175,195,100,30,makecol(255,180,180));
A First Look atANIMATION
x = max_x/2; y = max_y/2; vx = 2; vy = -3; while(!key[KEY_ESC]) { xold = x; yold = y; x = x + vx; y = y + vy; if(x<=radius || x>=max_x-radius) vx = -vx; if(y<=radius || y>=max_y-radius) vy = -vy; circle(screen,xold,yold,radius,BLACK); circle(screen,x,y,radius,BLUE); rest(20); }
x,y is the ball position (starts in the middle of the screen
the speed of the ball in the x and y directions - vx,vy
old position of ball
new position of ball
if ball reaches the edge, it bounces off (v = -v)
erase (undraw) old balldraw new ball
wait awhile (milliseconds)
Bouncing Ball Demo
Copy the folder named BouncingBall_Demo_01 from your CD to the Dev-Cpp folder on your computer.
Open this folder and then load the project BouncingBall_Demo_01.dev
Compile and Run this program
Modify the values of vx, vy and the value in the rest( ) function. With each change, run the program and notice the effect of your changes.
motion in x direction andy direction are kept separate
position of ball as a function of time is p = p0 + v0t + 1/2 at2
Note the scaryPhysics Formula
install_keyboard();while(!key[KEY_ESC]) { pxold = px; pyold = py; x = x + vx; y = y + vy; px = (int)x; py = (int)y; //watch out for sticky walls if(px<=radius || px>=max_x-radius) vx = -vx; if(py<=radius || py>=max_y-radius) vy = -vy; circle(screen,pxold,pyold,radius,BLACK); circle(screen,px,py,radius,BLUE); rest(20); if(key[KEY_LEFT]) vx = vx - 0.1; if(key[KEY_RIGHT]) vx = vx + 0.1; if(key[KEY_UP]) vy = vy - 0.1; if(key[KEY_DOWN]) vy = vy + 0.1; }
Making a Program Respond to User Keyboard Entry
keyboard entryarrow keys change the x and y velocity of the ball
Interactive Bouncing Ball Demo
Copy the folder named BouncingBall_Demo_02 from your CD to the Dev-Cpp folder of your computer
Open the project and run it.
Notice the effect of holding down one or more of the arrow keys.
End the program and review the source code for the user actions.
Modify the program and add key controls (such as the digit keys) to change the color or size of the ball.
circle(screen,px,py,radius,BLUE);
Allegro defines KEYS as,
A = KEY_A 1 = KEY_1 : Z = KEY_Z
play_sample(sample_filename, volume, panning, pitch, FALSE);
Sound
Allegro gives us an easy way to add sound to our game programs.
name of sample sound file to play
volume 0 to 255
speaker balance 0 to 255 (128 for equal balance)
frequency at which sample sound is played (1000 is normal)
looping (repeat sound) FALSE = no, TRUE = yes
SAMPLE *boing1;SAMPLE *boing2;if (install_sound(DIGI_AUTODETECT, MIDI_NONE, "") != 0) { allegro_message("Error initializing sound system"); return 1;}boing1 = load_sample("boing1.wav");boing2 = load_sample("boing2.wav");
Adding Sound to the Bouncing Ball
Before using the play_sample( ) function, we have to tell the computer which sounds we will be playing. Add this code to BouncingBall_Demo_02 near the top of main.cpp (just after install_keyboard( ) will be fine).
Copy the sound files boing1.wav and boing2.wav from the Sound Files folder into the BouncingBall_Demo_02 folder.
if (px<=radius || px>=max_x-radius){ vx = -vx; play_sample(boing1, 128, 128, 1000, FALSE);}
if (py<=radius || py>=max_y-radius){ vy = -vy; play_sample(boing2, 255, 128, 1000, FALSE);}
Now add the play_sample( ) functions to the bounce detection code. Since we are adding a second line of code to the if statements, we will need to add curley brackets to hold them. Otherwise the program will not know that the sound files should be played only when the conditional statement in the if( ) is true
After modifying and running your version of the Bouncing Ball, try running BouncingBall_Demo to compare. In this version we set the pitch based on the speed of the ball...
SAMPLE *sample1; SAMPLE *sample2; int panning = 128; int pitch = 1000; int volume = 128;
//initialize the program allegro_init(); install_keyboard(); install_timer(); set_gfx_mode(MODE, WIDTH, HEIGHT, 0, 0);
//install a digital sound driver if (install_sound(DIGI_AUTODETECT, MIDI_NONE, "") != 0) { allegro_message("Error initializing sound system"); return 1; }
WAV Sound Demoleft-right balance, volume, & pitch control
//display program informationtextout_ex(screen,font,"PlayWave Program (ESC to quit)",0,0,15,0);textprintf_ex(screen,font,0,10,15,0,"Snd Driver: %s",digi_driver->name);textout_ex(screen,font,"Playing clapping.wav...",0,20,15,0);textout_ex(screen,font,"Left,Right - Pan Left,Right",0,50,15,0);textout_ex(screen,font,"Up,Down - Pitch Raise,Lower",0,60,15,0);textout_ex(screen,font,"-,+ - Volume Down,Up",0,70,15,0);
//load the wave filesample1 = load_sample("evil_laugh.wav");sample2 = load_sample("clapping.wav");
if (!sample1 || !sample2) { allegro_message("Error reading wave file"); return 1;}
//play the sample with loopingplay_sample(sample1, volume, panning, pitch, TRUE);play_sample(sample2, volume, panning, pitch, TRUE);
while (!key[KEY_ESC]) { //change the panning if ((key[KEY_LEFT]) && (panning > 0)) panning--; else if ((key[KEY_RIGHT]) && (panning < 255)) panning++;
//change the pitch (rounding at 512) if ((key[KEY_UP]) && (pitch < 16384)) pitch = ((pitch * 513) / 512) + 1; else if ((key[KEY_DOWN]) && (pitch > 64)) pitch = ((pitch * 511) / 512) - 1;
//change the volume if (key[KEY_EQUALS] && volume < 255) volume++; else if (key[KEY_MINUS] && volume > 0) volume--;
//adjust the sample adjust_sample(sample1, 255-volume, 255-panning, pitch, TRUE); adjust_sample(sample2, volume, panning, pitch, TRUE);
//pause rest(5);}
destroy_sample(sample1);destroy_sample(sample2);remove_sound();
PongThe First Computer Game
We are going to look inside PONG, the first computer
game.
review Pong_Demo_01& Pong_Demo_02
Deconstructing Pong
game space
the game is played in a rectangular box
ball
the ball travels in a straight line until hitting an obstacle
ball bounces off top and bottom of game space
bounces off right face of left paddle and left face of right paddle
if ball encounters sides of game space point is scored and play restarts
left and right paddles
paddles stay on sides of game space can move up and down only
paddles can put "english" on ball if ball hits near the top or the bottom
scoreboard
keeps a record of players scores - first to 11 wins
init allegro
init
init variables
new game?
save old positiions
end loop
game loop
ball at top orbottom
ball hit paddle
ball miss paddle
quit game?
update scoreboard
players input
animate
score & reset
return ball
bounce ball
paddles at topor bottom stop paddle
exit allegro
Pong GameBlock Diagram
yes
no
// initialize game state padLeftX = 20; // left paddle x-position padRightX = SCREEN_W - 20; // right paddle x-position padLeftY = SCREEN_H/2; // left paddle y-position padRightY = SCREEN_H/2; // right paddle y-position bxi = SCREEN_W/2; // starting ball x-position byi = SCREEN_H/2; // starting ball y-position bvyi = 0; // starting ball y-velocity bvxi = 2; // starting ball x-velocity bx = bxi; // ball x-position by = byi; // ball y-position bvx = bvxi; // ball x-velocity bvy = bvyi; // ball y-velocity Lcount = 0; // left-player score Rcount = 0; // right-player score
Initialize Game State - PONG
// check for game quit if (key[KEY_ESC]) done = true; // save current paddle and ball positions before updates padLeftYold = padLeftY; padRightYold = padRightY; bxold = bx; byold = by; // update ball position bx += bvx; by += bvy;
// bounce ball off top and bottom of game space if (by <= 0 | by >= SCREEN_H) bvy = -bvy;
Top of Main Loop - PONG
// manage ball hitting left paddle if ((bx <= padLeftX + padWidth/2) & (abs(padLeftY - by)<=padHeight/2)) { bx = padLeftX + padWidth/2; bvx = - bvx; bvy = 0; if (padLeftY-by<-padHeight/5) bvy = + 1; if (padLeftY-by>padHeight/5) bvy = - 1; if (padLeftY-by<-padHeight/4) bvy = + 2; if (padLeftY-by>padHeight/4) bvy = - 2; }
// manage ball hitting right paddle if ((bx >= padRightX - padWidth/2) & (abs(padRightY - by)<=padHeight/2)) { bx = padRightX - padWidth/2; bvx = - bvx; bvy = 0; if (padLeftY-by<-padHeight/5) bvy = + 1; if (padLeftY-by>padHeight/5) bvy = - 1; if (padRightY-by<-padHeight/4) bvy = + 2; if (padRightY-by>padHeight/4) bvy = - 2; }
Manage Ball Hitting Paddle - PONG
if(padLeftY<padHeight/2) padLeftY = padHeight/2;
if(padLeftY>SCREEN_H - padHeight/2) padLeftY = SCREEN_H - padHeight/2;
if(padRightY<padHeight/2) padRightY = padHeight/2;
if(padRightY>SCREEN_H - padHeight/2) padRightY = SCREEN_H - padHeight/2;
Checking Game Space Limits
padHeight
padLeftY
(0,0)
?
After player inputs have been handled the new positions of the movable objects need to be checked to ensure that they are within the game space limits. What to do to keep the objects inside the game space depends on the object's function. For the paddles, you can just replace the new position with the limiting position as if it has hit a boundary.
// manage ball missing left paddle if (bx < padLeftX + padWidth/2) { rectfill(screen,0,0,SCREEN_W,SCREEN_H,BLACK); Rcount += 1; bx = bxi + SCREEN_W/3; by = byi; bvy = 0; bvx = -bvxi; } // manage ball missing right paddle if (bx > padRightX - padWidth/2) { rectfill(screen,0,0,SCREEN_W,SCREEN_H,BLACK); Lcount += 1; bx = bxi - SCREEN_W/3; by = byi; bvy = 0; bvx = bvxi; } // update scoreboard rectfill(screen, SCREEN_W/2-25,0,SCREEN_W/2+25,20,BLACK); textprintf_ex(screen, font, SCREEN_W/2-20, 10, 15, -1, "%d %d", Lcount, Rcount);
Manage Ball Passing Paddle - PONG
// manage user input for paddle movementif (key[KEY_A]) padLeftY -= padVy;if (key[KEY_Z]) padLeftY += padVy;if (key[KEY_K]) padRightY -= padVy;if (key[KEY_M]) padRightY += padVy;
Players Move Paddles Using A,Z and K,M Keys - PONG
// manage paddles touching boundary of game space if (padLeftY<padHeight/2) padLeftY = padHeight/2;
if (padLeftY>SCREEN_H - padHeight/2) padLeftY = SCREEN_H - padHeight/2;
if (padRightY<padHeight/2) padRightY = padHeight/2;
if (padRightY>SCREEN_H - padHeight/2) padRightY = SCREEN_H - padHeight/2;
Stop Paddles at Boundary of Game Space - PONG
// animate ball and paddlescirclefill(screen,bxold,byold,rad,BLACK);circlefill(screen,bx,by,rad,YELLOW);rectfill(screen,padLeftX-padWidth/2,padLeftYold-padHeight/2, padLeftX+padWidth/2,padLeftYold+padHeight/2,BLACK);rectfill(screen,padRightX-padWidth/2,padRightYold-padHeight/2, padRightX+padWidth/2,padRightYold+padHeight/2,BLACK);rectfill(screen,padLeftX-padWidth/2,padLeftY-padHeight/2,padLeftX+ padWidth/2,padLeftY+padHeight/2,GREEN);rectfill(screen,padRightX-padWidth/2,padRightY-padHeight/2,padRightX+ padWidth/2,padRightY+padHeight/2,RED);rest(1);
Animate Game - PONG
Adding some Excitement with a Bit of Randomness
Version 01 of Pong_Demo is functional but BORING! Lets add some excitement by increasing the speed of the return ball each time the ball hits the center of the paddle.
We can also randomize the speed of the ball a little every now and then.
Insert the following lines of code at the bottom of the if( ) that deals with the ball hitting the paddle (both left and right).
if (bvy == 0) bvx -= 1;if (bvx<-8) bvy += rand() % 4 - 2;if (rand() % 100 > 94) bvy += rand() % 4 - 2;
You can skip the exercise and run Pong_Demo_02 to see the changes.
KING PONG
Now run King_Pong to see the value of adding sound to your game.
(0,0)
(0,SCREEN_H)(SCREEN_W,SCREEN_H)
(SCREEN_W,0)
maintain 4 to 3 aspect ratio
Game Space Layout
Keyboard Input Demo - Displays an open circle on screen. Circle can be moved using the arrow keys. The diameter of the circle can be changed using the Page-Up and Page-Down keys. Movement of circle is limited to keep circle on screen.
Mouse Graphics Demo - The program demonstrates the use of the mouse in Allegro. Mouse movement moves a spot on the screen. Pressing the LEFT, RIGHT, or both mouse buttons changed the color of the spot.
Gamepad Demo - A USB game controller must be plugged in for this program to function. Program detects the game pad and shows a simple graphical display indicating the number of joysticks (2-axis) and sliders (1-axis) controls, and the number of buttons including the front fire buttons. Program moves a yellow spot in screen, controlled by 1st 2-axis control, the size of the spot is changed by pressing button 7 and 8 and six different sound events are invoked by pressing buttons 1 through 6.
Computer Input Demo Programs
allegro_init();install_keyboard();
Keyboard Demorun keyboard_input_demo
Mouse Input DemoMouse_Graphics_Demo
allegro_init();install_mouse();
Joystick Input Demojoystick_demo & joystick_graphics_demo
plug in generic gamepad (USB) first
allegro_init();install_joystick(JOY_TYPE_AUTODETECT);
GamePad Graphics Demogamepad_demo
while(!keypressed()){ //graphics loop poll_joystick(); xold = x; yold = y; radius_old = radius; if(joy[0].stick[0].axis[0].pos<0) x = x - 2; if(joy[0].stick[0].axis[0].pos>0) x = x + 2; if(joy[0].stick[0].axis[1].pos<0) y = y - 2; if(joy[0].stick[0].axis[1].pos>0) y = y + 2; if(joy[0].button[6].b>0) radius = radius - 1; if(joy[0].button[7].b>0) radius = radius + 1; if(x>max_x) x = max_x; if(x<0) x = 0; if(y>max_y) y = max_y; if(y<0) y = 0; if(radius<2) radius = 2; if(radius>100) radius = 100; if(xold!=x || yold!=y || radius_old!=radius) circlefill(screen,xold,yold,radius_old,BLACK); circlefill(screen,x,y,radius,YELLOW);
GamePad Graphics Control DemoSample Source Code
BITMAP *buffer;::
int ret = set_gfx_mode(GFX_AUTODETECT_WINDOWED, max_x, max_y, 0, 0);if (ret!=0){ allegro_message(allegro_error); return 1;}buffer = create_bitmap(SCREEN_W, SCREEN_H);
::
clear_bitmap(buffer);blit(buffer, screen, 0, 0, 0, 0, SCREEN_W, SCREEN_H);
Double Buffering
The purpose of double buffering is to eliminate or reduce the flicker in an animation due to drawing directly on the display being viewed (screen). Instead we will draw on a bitmap elsewhere in memory and then transfer (blit) the completed image to the screen in one operation.
Draw_Sprite_Demo
Demonstrates loading and displaying background image, loading, animation and scaling of sprites, and blitting to replace background under moving sprite. Includes loading and playing sound with volume as a function of distance from a specific point. Movement of sprite is through arrow keys. Sound is invoked with spacebar, when Carman sprite is close to Chef. Special Features: A simple 3D effect is achieved by scaling sprite as it moves up and down in scene.
Sample Graphics Output
int main(){ char *filename = "southpark_town.bmp"; BITMAP *bkg_image; BITMAP *cartman;
int x, y;double scale;int xold,yold;int vol = 128;int max_x = 640;int max_y = 480;
SAMPLE *chef_hello; int volume = 255; int pan = 128; int pitch = 1000;
//initialize the program allegro_init();
install_keyboard();set_color_depth(16);
set_gfx_mode(GFX_AUTODETECT_WINDOWED, max_x, max_y, 0, 0); if (install_sound(DIGI_AUTODETECT, MIDI_NONE, "") != 0) { allegro_message("Error initializing sound system"); return 1; }
Draw Sprite Demo
//load the wave file chef_hello = load_sample("chef-hello_there_children.wav"); bkg_image = load_bitmap(filename, NULL); if (!bkg_image) { set_gfx_mode(GFX_TEXT, 0, 0, 0, 0); allegro_message("Error loading %s", filename); return 1; } blit(bkg_image, screen, 0, 0, 0, 0, SCREEN_W, SCREEN_H);
//rectfill(screen,0,0,max_x,max_y,GREEN); //print some status information textprintf_ex(screen,font,0,0,WHITE,0,"Resolution = %ix%i", SCREEN_W, SCREEN_H); textprintf_ex(screen, font, 0, 10, WHITE,0,"Color depth = %i", bitmap_color_depth(screen));
//load the cartman bitmap cartman = load_bitmap("cartman.bmp", NULL); x = SCREEN_W/2 - cartman->w/2; y = SCREEN_H/2;
//main loopwhile (!key[KEY_ESC]){ scale = (max_y/2 + 4.0*(double)(y-max_y/2))/(double)(max_y/2); stretch_sprite(screen, cartman, x, y, scale*cartman->w,scale*cartman->h);
textprintf_ex(screen,font,0,20,WHITE,0, "Location = %ix%i", x, y); rest(20); xold = x; yold = y; if(key[KEY_UP]) y = y - 1; if(key[KEY_DOWN]) y = y + 1; if(key[KEY_LEFT]) x = x - 2; if(key[KEY_RIGHT])x = x + 2; if(xold!=x || yold!=y) blit(bkg_image, screen, x, y, x, y, scale*cartman->w,scale*cartman->h); if(x>max_x-cartman->w-20) x = max_x-cartman->w-20; if(x<-20) x = -20; if(y>max_y-cartman->h) y = max_y-cartman->h; if(y<max_y/2) y = max_y/2; vol = 255 - abs(x-425) - abs(y-250); if(vol<0) vol = 0; if(key[KEY_SPACE] && vol>10) { stop_sample(chef_hello); play_sample(chef_hello,vol,128,1000,FALSE); rest(100); }}
Rotating Sprites Demo
rotate_sprite(buffer,sprite,x,y,itofix(ang));
ang is the angle of rotation in allegro units
0 - 360 degrees = 0 - 255 allegro angle units
Angles (ang) must be converted from integer to fixed precision type values using the itofix( ) function included in the allegro library.
Fifty-Two Pickuprun CardDemo
As an example of accessing sprites from a two-dimensional sprite sheet, we will drop cards randomly onto the screen from a 52-card deck. Actually we will be selecting card images at random, so there will be many more that 52 cards displayed.
950
392
98
73
(rank*73,suit*98)
rank = (0..12)
suit = (0..3)
Managing the Cards Sprite
void main(void){ int cardwidth = 73; int cardheight = 98; int width = 1180; int height = 720; char *filename = "cards_orig.bmp"; BITMAP *cards; BITMAP *buffer; allegro_init(); install_keyboard(); set_color_depth(16); int ret = set_gfx_mode(GFX_AUTODETECT_WINDOWED, width, height,0,0); cards = load_bitmap(filename, NULL); buffer = create_bitmap(width,height); clear_bitmap(buffer); srand(time(NULL)); while(!key[KEY_ESC]) { blit(cards,buffer,rand()%13*cardwidth,(rand()%4)*cardheight, rand()%(width-cardwidth),rand()%(height-cardheight), cardwidth,cardheight); blit(buffer,screen,0,0,0,0,width,height); } allegro_exit();}END_OF_MAIN()
Complete Source Code - 52 Pick-Up
Sample Run
Translucent Sprites
Translucent sprites are used for many special effects. The principle behind translucency is to combine the r,g,b values of two pixels occupying the same location in a bitmap. Normally you replace the background pixels with the overlaying sprite pixels using the blit( ) function. We will set a to a value between 0.0 and 1.0 to represent the fraction of the foreground pixel to be used, so (1-a) will be the amount of the background pixel used.
int pixbk, rbk, gbk, bbk;int pixsp, rsp, gsp, bsp;
pixbk = getpixel(bkgimage,i,j);pixsp = getpixel(spriteimg,k,m);
rbk = getr(pixbk); rsp = getr(pixsp); gbk = getg(pixbk); gsp = getg(pixsp);bbk = getb(pixbk); bsp = getb(pixsp);
rbk = alpha*rbk + (1.0-alpha)*rsp;gbk = alpha*gbk + (1.0-alpha)*gsp;bbk = alpha*gbk + (1.0-alpha)*bsp;
pixbk = makecol(rbk,gbk,bbk);
Card Drop Screen SaverCardScreenSaver demos translucent sprites
In this example we will modify the previous card demo to cause the cards to fade out after they have been dropped onto the screen. This demo woul make a good screen saver. After each card drop will will reduce the brightness of every pixel of the screen image using the function dimmer( ).
void dimmer(void){ int pix; int r,g,b; for(int i=0;i<width;i++) for(int j=0;j<height;j++) { pix = getpixel(buffer,i,j); r = getr(pix); g = getg(pix); b = getb(pix); r -= 8; g -= 8; b -= 8; if(r<0) r=0; if(g<0) g=0; if(b<0) b=0; pix = makecol(r,g,b); putpixel(buffer,i,j,pix); }}
while(!key[KEY_ESC]) { blit(cards,buffer,rand()%13*cardwidth,(rand()%4)*cardheight, rand()%(width-cardwidth),rand()%(height-cardheight), cardwidth,cardheight); dimmer(); blit(buffer,screen,0,0,0,0,width,height); } allegro_exit();
Modified Main Loop
Sample Run
Animated Sprite Demouses Prince of Persia Sprite Sheet
Sprite Sheet
728 x 90 pixelseach image region is 728/13 = 56 x 90 pixelsdefault transparency color is magenta rgb = (255,0,255)
num_steps = 0; while(!key[KEY_ESC]) { for(int i=0;i<13;i++) { move = num_steps*step_size; blit(bkg_image, buffer, 660-move-10, 380, 660-move-10, 380, 76, 90); masked_blit(sprite_sheet,buffer, i*56,0,660-move,380,56,90); blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H); num_steps +=1; if(move>720) num_steps = 0; rest(80); } }
selects the proper segment of thesprite sheet to display
covers old sprite with the proper region ofthe background image
char *backname = "BlueBkg.bmp"; char *spritename = "alladin.bmp"; BITMAP *bkg_image; BITMAP *sprite_sheet; BITMAP *buffer; int sprite_width = 56; int sprite_height = 90; int step_size = 5; int num_steps; int move; //initialize the program allegro_init();
install_keyboard();set_color_depth(16);
set_gfx_mode(GFX_AUTODETECT_WINDOWED, 640, 480, 0, 0); bkg_image = load_bitmap(backname, NULL); if (!bkg_image) { set_gfx_mode(GFX_TEXT, 0, 0, 0, 0); allegro_message("Error loading %s", backname); return 1; } sprite_sheet = load_bitmap(spritename,NULL); if(!sprite_sheet) { set_gfx_mode(GFX_TEXT,0,0,0,0); allegro_message("Error loading %s", spritename); return 1; }
buffer = create_bitmap(SCREEN_W, SCREEN_H);clear_bitmap(buffer);blit(bkg_image,buffer,0,0,0,0,640,480);masked_blit(sprite_sheet,buffer,0,0,15,130,728,90); num_steps = 0;while(!key[KEY_ESC]){ for(int i=0;i<13;i++) { move = num_steps*step_size; blit(bkg_image, buffer, 660-move-10, 380, 660-move-10, 380, 76, 90); masked_blit(sprite_sheet,buffer, i*56,0,660-move,380,56,90); blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H); num_steps +=1; if(move>720) num_steps = 0; rest(80); }}destroy_bitmap(bkg_image);destroy_bitmap(sprite_sheet);allegro_exit();return 0;
Sprite Sheet for The Prince of Persia
Creating a Sprite Image
Tank Composed ofPower Point 3D Objects
finished sprite sheet with transparency
reference image
In PowerPoint the objects are movable, so animations are much simpler to create. Make sure that each copy of the sprite is equally spaced in the sprite sheet.
sprite_width = 98 pixels
Tank Sprite Demo
Implements an animated sprite of a tank with a separately moveable gun tube (barrel) on the turret. Tank motions is controlled using the Z and X keys.
Gun barrel elevation is controlled using the Q and A keys. Uses a sprite sheet created using Power Point and Paint Shop Pro (see Lecture 9 for more info).
Demonstrates the integration of multi-part sprites with rotate_sprite( ), masked_blit( ) and normal blit( ) functions.
Special Features: Sounds are integrated with sprite actions and left-to-right panning is used to adjust the sound levels in each speaker to correspond to sprite position.
Z and X move tank backward and forward
Q and A raise and lower turret gun
Sample Output
Z - move backwardX - move forward
Q - barrel upA - barrel down
char *backname = "BlueBkg.bmp"; char *spritename = "tank_sprite_sheet_sm.bmp"; char *turretname = "turretsprite.bmp"; BITMAP *bkg_image; BITMAP *sprite_sheet; BITMAP *turret_sprite; BITMAP *buffer; SAMPLE *backsound; SAMPLE *tanksound; SAMPLE *turretsound; int sprite_width = 98; int sprite_height = 60; int step_size = 5; int num_steps,i; int move = 0; int tankpan; int turret_ang = 255; bool tankon = false; bool turreton = false;
Tank Sprite Demo Setup
Frames of moving tank are separated by 98 pixels horizontally and fit in a 98 x 60 pixel rectangle.
The smallest move increment is set to 5 pixels. The horizontal position of the tank is set by,
move = num_steps * step_size
//initialize the programallegro_init();install_keyboard();set_color_depth(16);set_gfx_mode(GFX_AUTODETECT_WINDOWED, 760, 480, 0, 0); bkg_image = load_bitmap(backname, NULL);sprite_sheet = load_bitmap(spritename,NULL);turret_sprite = load_bitmap(turretname,NULL); buffer = create_bitmap(SCREEN_W, SCREEN_H);clear_bitmap(buffer);blit(bkg_image,buffer,0,0,0,0,760,480); //install a digital sound driverif (install_sound(DIGI_AUTODETECT, MIDI_NONE, "") != 0) { allegro_message("Error initializing sound system"); return 1;} backsound = load_sample("dead_wind_loop.wav");tanksound = load_sample("tankgo.wav");turretsound = load_sample("turret.wav");play_sample(backsound, 128, 128, 1000, TRUE);
Loading Bitmaps and WAV Files
i = 0;num_steps = 0;
rotate_sprite(buffer,turret_sprite,36,413,itofix(255));
masked_blit(sprite_sheet,buffer, 15,10, 15, 405, sprite_width,sprite_height);
blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H);
i=0 i=1 i=2 i=3
Initial Position
while(!key[KEY_ESC]){ // barrel up
// barrel down // tank backward // tank forward // turn off tanksound //turn off turretsound // draw and display next frame}
Actions in Main Game Loop
// barrel up if(key[KEY_Q]){ turret_ang -= 1; if(turret_ang<200) turret_ang=200; if(!turreton) { play_sample(turretsound,255,tankpan,1000,TRUE); turreton = true; } adjust_sample(turretsound,255,tankpan,1000,TRUE);} // barrel downif(key[KEY_A]){ turret_ang += 1; if(turret_ang>255) turret_ang = 255; if(!turreton) { play_sample(turretsound,255,tankpan,1000,TRUE); turreton = true; } adjust_sample(turretsound,255,tankpan,1000,TRUE);}
Turret Gun Actions
Turret Gun Tube Rotation
rotate_sprite(turret_sprite, buffer,destx,desty,itofix(ang));
255
192
ang
turret_sprite is twice as long as barrel because axis of rotation is at the center of the image and we wish to rotate barrel about one end.
placement of barrel in destination image is offset so that back end of barrel is aligned with front of tank turret.
// tank backwardif(key[KEY_X]){ i = (i+1) % 4; num_steps +=1; move = num_steps*step_size; tankpan = 255*move/SCREEN_W; if(!tankon) { play_sample(tanksound,255,tankpan,1000,TRUE); tankon = true; } adjust_sample(tanksound,255,tankpan,1000,TRUE);} // tank forwardif(key[KEY_Z]){ i = i-1; if(i<0) i=3; num_steps -=1; move = num_steps*step_size; tankpan = 255*move/SCREEN_W; if(!tankon) { play_sample(tanksound,255,tankpan,1000,TRUE); tankon = true; } adjust_sample(tanksound,255,tankpan,1000,TRUE);}
Tank Motion Actions
// turn off tanksoundif(!key[KEY_X] && !key[KEY_Z]){ stop_sample(tanksound); tankon = false;} // turn off turretsoundif(!key[KEY_A] && !key[KEY_Q]){ stop_sample(turretsound); turreton = false;} // draw and display next frameblit(bkg_image, buffer, 0,0,0,0,SCREEN_W,SCREEN_H);rotate_sprite(buffer,turret_sprite,36 + move,413,itofix(turret_ang));masked_blit(sprite_sheet,buffer, 15+i*sprite_width, 10, 15 + move, 405, sprite_width,sprite_height); blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H);rest(80);
Stop Sounds Actions and Display
Collision Detection - Atomic FirefliesCollision_Detection_Demo_02
for(int k=0;k<Num-1;k++) for(int m=k+1;m<Num;m++) collide(k,m);
void collide(int k, int m){ if([collision_check]) { // handle collision }}
double dist(int k, int m){ return sqrt(pow((ball[k].x-ball[m].x),2.0) + pow((ball[k].y-ball[m].y),2.0));}
Note: Straight-line distance is not the most efficient method for detecting collisions. Compare with hit( ) function shown later.
Collision Detection Demo
Program creates an array of small moving objects that bounce around the screen. For each frame, the location of all pairs of objects are compared. When a pair is detected to have collided, the event is marked with an explosion event. The explosion event begins a sixteen frame explosion sequence with its position and velocity equal to the everage position and velocity of the pair of colliding objects. Special Features: Demonstrates display of multiple animated events.
Collision_Detection_Demo uses left and right arrow to change the number of fireflies on screen.
Collision Detection - Atomic Fire Flies
struct ball_state { double x; double y; double vx; double vy; int px; int py; int pxold; int pyold;} ball[100];
struct fire_state { double x; double y; double vx; double vy; int count;} fire[100];c
Moving Balls and Explosion Struct Lists
void draw_explosion(int x, int y, int& c){ masked_blit(explosion,buffer,(c % 4)*64,(c/4)*64,x-32,y-32,64,64); c += 1;}
256 x 256 pixel imageof explosion
col = c % 4row = c / 4
sprite images are 64 x 64 pixels
Extracting Frames from 2D Sprite
Sometimes sprite sheets are arranged in two-dimensional arrays of images. In these cases we need to determine in which row and column each image is placed so that they can be accessed and displayed in the proper sequence.
for(int k=0;k<bcount-1;k++) for(int m=k+1;m<bcount;m++) collide(k,m); for(int q=0;q<fcount;q++){ if(fire[q].count==0) play_sample(explode[rand()%4],rand()%56+200,rand()%256, 800+rand()%400,FALSE); draw_explosion((int)fire[q].x,(int)fire[q].y,fire[q].count); fire[q].x += fire[q].vx; fire[q].y += fire[q].vy;}
remove_fireballs();
Managing Multiple Animated Sprites
Successive frames of two or more animated sprites should be displayed concurrently. In this example the frame count (fcount) is set to 0 by the draw_explosion( ) function so it can be removed from the active sprite list, fire[ ].
draw_explosion( ) increments frame countof the explosion sprites
for(int i = 0; i<bcount;i++){ ball[i].pxold = ball[i].px; ball[i].pyold = ball[i].py; ball[i].x = ball[i].x + ball[i].vx + rand()%4-2; ball[i].y = ball[i].y + ball[i].vy + rand()%4-2; ball[i].px = (int)ball[i].x; ball[i].py = (int)ball[i].y;
if(ball[i].px<=radius || ball[i].px>=max_x-radius) { ball[i].vx = -ball[i].vx; if(ball[i].x>=radius) ball[i].x=(double)(max_x-radius); else ball[i].x=(double)radius; } if(ball[i].py<=radius || ball[i].py>=max_y-radius) { ball[i].vy = -ball[i].vy; if(ball[i].y>=radius) ball[i].y=(double)(max_y-radius); else ball[i].y=radius; } circlefill(buffer,ball[i].pxold,ball[i].pyold,radius,ORANGE); circlefill(buffer,ball[i].px,ball[i].py,radius,BLUE);}
Managing An Array of Moving Objects
int hit(int k, int m, int range){ int xsep; int ysep; xsep = (int) (ball[k].x - ball[m].x); ysep = (int) (ball[k].y - ball[m].y); if(xsep<range && xsep>-range && ysep<range && ysep>-range) return 1; else return 0;}
void collide(int k, int m){ if(hit(k,m,close_enough)) { fcount+=1; fire[fcount-1].x = (ball[k].x + ball[m].x)/2.0; fire[fcount-1].y = (ball[k].y + ball[m].y)/2.0; fire[fcount-1].vx = (ball[k].vx + ball[m].vx)/2.0; fire[fcount-1].vy = (ball[k].vy + ball[m].vy)/2.0; fire[fcount-1].count = 0; }}
Detecting Collisions and Managing the Collision List
void remove_fireballs(void){ int inc = 0; int dec = 0; bool done = (fcount<=0); while(!done) { if(fire[inc].count>15 && dec<fcount) dec += 1; if(dec<fcount) { fire[inc] = fire[dec]; if(fire[inc].count<=15) { inc += 1; dec += 1; } } done = (dec>=fcount); } fcount = inc;}
Removing Completed Fireballs from the Fire[ ] List
fire[.] list is scanned and all members with count>15 are dropped.
fcount is reduced by the number of members eliminated.
12
2
2
16
4
16
16
7
8
inc dec12
2
4
7
8
inc dec
16
16
7
8
fire[]
Setting the World View
Scrolling
Defining Fixed Objects and Their Actions/Reactions Background Foreground Block Movable/Breakable
Defining Characters and other Animated Objects Player Opponents Animated Interactive Object
Loading Maps
Controlling Display
Side Scrolling Games
Scrolling
Horizontal (or vertical) scrolling gives us the freedom to implement a game world that is much larger than our display screen. Through the use of double buffering and blitting we can smoothly move through the game always displaying a view of the game centered on the action and our character.
Scanning a Panoramic ImageA Step Toward Horizontal Scrolling
while(!key[KEY_ESC]){ if(key[KEY_LEFT]) { blitx -= 3; if(blitx<0) blitx = 0; } if(key[KEY_RIGHT]) { blitx += 3; if(blitx+SCREEN_W>bkgwidth) blitx = bkgwidth - SCREEN_W; } blit(bkgimage,buffer,blitx,blity,0,0,SCREEN_W,SCREEN_H); blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H);}
blitx and blity define the corner of the portion of the bkgimage that will be displayed.
bounding conditions are used to ensure that the display window stays inside the limits of the bkgimage.
display screen
// Horizontal Scrolling Demo 1
#include <allegro.h>
int max_x = 640; int max_y = 480; int blitx = 0; int bkgwidth = 7249; int bkgheight = 529; int blity = 0;
char *filename = "talafar.bmp"; BITMAP *bkgimage; BITMAP *buffer;
void main(void){ allegro_init(); install_keyboard(); set_color_depth(16); int ret = set_gfx_mode(GFX_AUTODETECT_WINDOWED, max_x, max_y, 0, 0); bkgimage = load_bitmap(filename,NULL); buffer = create_bitmap(SCREEN_W, SCREEN_H); while(!key[KEY_ESC]) { if(key[KEY_LEFT]) { blitx -= 3; if(blitx<0) blitx = 0; } if(key[KEY_RIGHT]) { blitx += 3; if(blitx+SCREEN_W>bkgwidth) blitx = bkgwidth - SCREEN_W; } blit(bkgimage,buffer,blitx,blity,0,0,SCREEN_W,SCREEN_H); blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H); rest(1); }}END_OF_MAIN()
The Central Object
int max_x = 640;int max_y = 529;int chxmin = 10;int chxmax = 7239;int chymin = 0;int chymax = 519;int bkgwidth = 7249;int bkgheight = 529;int blitx = 320;int blity = 40;
double chx,chy,chvx,chvy,chax,chay;double chvxmax = 20.0;double chvxmin = -20.0;double bounce = 0.8;double dt = 0.1;
x
y
chx - x positionchy - y positionchvx - x velocitychvy - y velocitychax - x accelerationchay - y acceleration
Motion in a Constant Gravitational Field
Separate the motion in the x direction (horizontal) from motion in the y direction (vertical). Gravity acts in the negative y direction (-9.8 m/s2). There is no force in the x direction on a moving object (without friction).
x
y
x, y - object locationvx, vy - object velocityay - object acceleration due to gravity = -9.8 meters/second/second.
chx = 30.0;chy = (double)chymax;chvx = 0.0; chvy = 0.0;chay = 9.8; chax = 0.0;
chvy = chvy + chay*dt;chvx = chvx + chax*dt;chy = chy + chvy*dt + 0.5*chay*dt*dt;chx = chx + chvx*dt + 0.5*chax*dt*dt;
if(key[KEY_LEFT]) { chax -= 1.0; if(chax<-5.0) chax = -5.0; }
if(key[KEY_RIGHT]) { chax += 1.0; if(chax>5.0) chax=5.0; }
main loop
Motion Controlled by Acceleration
blitx = (int)chx - SCREEN_W/2;blity = (int)chy - SCREEN_H/2;
if(blitx<0) blitx = 0;if(blitx+SCREEN_W>bkgwidth) blitx = bkgwidth - SCREEN_W;
if(blity<0) blity = 0;if(blity+SCREEN_H>bkgheight) blity = bkgheight - SCREEN_H;
circlefill(bkgimage,(int)chx,(int)chy,8,makecol(255,0,0));blit(bkgimage,buffer,blitx,blity,0,0,SCREEN_W,SCREEN_H);blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H);
Positioning the Display Screen in the World View
First the display screen is centered on the ball and then its horizontal and/or vertical position is shifted as needed to keep the display inside the world view.
Drawing a Bitmap - Sample Output
#include <allegro.h>int main(void){ char *filename = "game_bkg.bmp"; BITMAP *image; int ret; allegro_init(); install_keyboard(); set_color_depth(16); ret = set_gfx_mode(GFX_AUTODETECT_WINDOWED, 640, 480, 0, 0); if (ret != 0) { allegro_message(allegro_error); return 1; } //load the image file image = load_bitmap(filename, NULL); if (!image) { set_gfx_mode(GFX_TEXT, 0, 0, 0, 0); allegro_message( "Error loading %s" , filename); return 1; } //display the image blit(image, screen, 0, 0, 0, 0, SCREEN_W, SCREEN_H); //done drawing--delete bitmap from memory destroy_bitmap(image); //display video mode information textprintf_ex(screen,font, 0, 0, 1, -1, "%dx%d" ,SCREEN_W,SCREEN_H); //wait for keypress while (!keypressed()); allegro_exit(); return 0;}END_OF_MAIN()
Loading a Bitmap
Sample Run
Embedding Fixed Objects
vpix
hpix
map arraynrows
ncols
game bkg image
We can associate a text array with the game world specifying the location of fixed sprites and other game objects. The size of each sprite region in pixels is given by,
Each region will be represented by an integer in the map array. The value of the integer will determine the properties of the object; such as, movable, breakable, background, foreground, etc...
spwidth = hpix/ncols
spheight = vpix/nrows
Sprite Width = = 29 pixels
Sprite Height = = 20 pixels
Map Array Details
0
0
0
0
0 0 0
0
0
29 x 20 pixels
250
281 2
7250 250
56028
0 - no sprite
1 - background sprite
2 - block (immovable)
3 - movable
4 - breakable
5 - other objects (such as ramps and pits).
#include <fstream.h>
struct cell{ int sprnum; int block; int breakable; int row; int col;}map[28][250];
void load_map(void){ ifstream inFile; inFile.open("map.dat"); for(int r=0;r<nrows;r++) for(int c=0;c<ncols;c++) inFile >> map[r][c].sprnum; inFile.close();}
Loading Map Array
Displaying the Map Array Cells in the Game World View
load_map(); for(int r = 0;r<nrows;r++){ for(int c = 0;c<ncols; c++) { cnum = map[r][c].sprnum; if(cnum == 0) col = BLUE; if(cnum == 1) col = GREEN; if(cnum == 2) col = RED; if(cnum == 3) col = YELLOW; rectfill(bkgimage, c*pwidth+2, r*pheight+2, (c+1)*pwidth-3, (r+1)*pheight-3,col); }}
leaves some spacearound each cell
pwidth = width of cell in pixelspheight = height of cell in pixels
struct block{ int xmin; int xmax; int ymin; int ymax;}blocks[100];
for(int r = 0;r<nrows;r++) for(int c = 0;c<ncols;c++) if(map[r][c].sprnum==2) { blocks[numblocks].xmin = pwidth*c; blocks[numblocks].xmax = pwidth*(c+1); blocks[numblocks].ymin = pheight*r; blocks[numblocks].ymax = pheight*(r+1); numblocks += 1; }
Building a List of Blocking Cells
defines the limitseach blocking cell
When ball region is inside block a collision is detected. Since there the ball can be in only one place a hit is set and all other block tests are suspended for this moment in the game.
We must also determine which surface of the block the ball has contacted. In this example we use the closest edge.
Warning: When there is a tie, odds things can happen. We'll refer to these anomalies as "special features" of the game. :-)
Managing Collisions
hit = false;for(int i=0;i<numblocks;i++){ if(inside(chx,chy,sep,blocks[i]) && !hit) { hit = true; dtime = 0; diffxleft = abs(((int)chx+sep) - blocks[i].xmin); diffxright = abs(((int)chx-sep)-blocks[i].xmax); diffytop = abs(((int)chy+sep) - blocks[i].ymin); diffybottom = abs(((int)chy-sep) - blocks[i].ymax); diffx = min(diffxleft,diffxright); diffy = min(diffytop,diffybottom); if(diffx<diffy) { chvx = - chvx; if(diffxleft<diffxright) chx = blocks[i].xmin - sep; else chx = blocks[i].xmax + sep; } else { chvy = - chvy; if(diffytop<diffybottom) chy = blocks[i].ymin - sep; else chy = blocks[i].ymax + sep; } }}
Code for Managing Collisions with Blocks
hstart = ((int)chx-pwidth)/pwidth;hfinish = ((int)chx+pwidth)/pwidth;vstart = ((int)chy-pheight)/pheight;vfinish = ((int)chy+pheight)/pheight;
if(hstart<0) hstart = 0;if(hfinish>ncols) hfinish = ncols;if(vstart<0) vstart = 0;if(vfinish>nrows) vfinish = nrows;for(int r=vstart;r<=vfinish;r++) for(int c=hstart;c<=hfinish;c++) { cnum = map[r][c].sprnum; if(cnum == 0) col = BLUE; if(cnum == 1) col = GREEN; if(cnum == 2) col = RED; if(cnum == 3) col = YELLOW; rectfill(bkgimage, c*pwidth+2, r*pheight+2, (c+1)*pwidth-3, (r+1)*pheight-3,col); }
Redrawing Background Cells
Sample Displays
x0 = 0 x1 = 2x x2 = 4x x3 = 2xy0 = 0 y1 = -x y2 = 0 y3 = x
Laying Down the Base
Nrow
bitmap
Ncol
2x
x
tcol = (Ncol - c)/Ncol
xstart = tcol*x0 + (1-tcol)*x1
ystart = tcol*y0 + (1-tcol)*y1
xfinish = tcol*x3 + (1-tcol)*x2
yfinish = tcol*y3 + (1-tcol)*y2
trow = (Nrow - r)/Nrow
x = trow*xstart + (1-trow)*xfinish
y = trow*ystart + (1-trow)*yfinish
(x2y2)
(x1y1)
(x3y3)
(x0y0)
3D Modeling byOrthographic Projection
Classic Isometric (3/4) View
x/2 pixels
Alternative Methods for Surface Transformation
px,py
bx,by
x pixels
Nro
w
Ncol
2/,2/0
21
210
210
02/12/,, sizesizesizebysizebxpypx
021
42
22
M =
Diablo II
Diablo II - Zoom
Diablo II - Level Editor Detail
Lessons Learned
There are limits to what we are able to cover in this workshop. If your dream is to create a Massive Multiplayer Role-Playing Game (MMRPG), you will have to take solace in the fact that the lessons learned in this workshop apply directly to game development projects that are much bigger than can be accomplished here.
Understanding the physics of motion and body on body iterations is the same for all applications.
The incorporation of and manipulation of sound applies to the simple single-player game as well as the larger multiplayer game.
The techniques of animation can be applied equally well to an animated sprite as to a intro/segway video sequence.
The methods to maintain real-time interactions as the complexity of the game scene varies are the same for any level of complexity.
The skills developed in creating an enjoyable single-player game are essential for development of an (MMRPG).