(C++) SDL example 4: moving a square in a 2D OpenGL environment

 

This SDL example shows a sprite moving a over a background, like this screenshot (png).

 

Operating system: Ubuntu

IDE: Qt Creator 2.0.0

Project type: Qt4 Console Application

Selected required modules: QtCore

Compiler: G++ 4.4.1

Additional libraries: SDL, OpenGL, Boost

 

 

 

 

 

Qt project file

 

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#------------------------------------------------- # # Project created by QtCreator 2010-07-17T14:57:33 # #------------------------------------------------- QT += core QT -= gui TARGET = CppSdlExample4 CONFIG += console CONFIG -= app_bundle TEMPLATE = app LIBS += -L/usr/local/lib -lSDL LIBS += -L/usr/local/lib -lGL SOURCES += main.cpp

 

 

 

 

 

Source code

 

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#include <cassert> #include <cstdlib> #include <vector> #include <boost/timer.hpp> #include <SDL/SDL.h> #include <SDL/SDL_opengl.h> int main() {   const int screen_width = 320;   const int screen_height = 200;   //Initialization   if( SDL_Init( SDL_INIT_VIDEO) < 0 )   {     assert(!"Assume SDL initialization does not fail");   }   //Perform SDL_Quit at program exit   std::atexit(SDL_Quit);   const int bits_per_pixel = 32;   if( !SDL_SetVideoMode( screen_width, screen_height, bits_per_pixel, SDL_OPENGL ))   {     assert(!"Assume SDL video mode setting does not fail");   }   //Initialize OpenGL   glClearColor( 0, 0, 0, 0 );   glMatrixMode( GL_PROJECTION );   glLoadIdentity();   glOrtho( 0, screen_width, screen_height, 0, -1, 1 );   glMatrixMode( GL_MODELVIEW );   glDisable(GL_DEPTH_TEST); //In 2D there is no need for a depth test   glLoadIdentity();   if( glGetError() != GL_NO_ERROR )   {     assert(!"Assume OpenGL initialization does not fail");   }   //Set up sprite   const int sprite_width = 10;   const int sprite_height = 10;   int sprite_x = (screen_width / 2) - (sprite_width / 2);   int sprite_y = (screen_height / 2) - (sprite_height / 2);   int sprite_dx = 1;   int sprite_dy = 1;   const int frames_per_second = 60;   const int ticks_per_second = 1000 / frames_per_second;   while(1)   {     //Use timer to keep frame rate constant     boost::timer timer;     //Handle events     SDL_Event event;     SDL_PollEvent( &event );     if( event.type == SDL_QUIT ) break;     //Move the square     sprite_x+=sprite_dx;     sprite_y+=sprite_dy;     //Make the square bounce     if (sprite_x < 0 || sprite_x + sprite_width > screen_width ) sprite_dx = -sprite_dx;     if (sprite_y < 0 || sprite_y + sprite_height > screen_height ) sprite_dy = -sprite_dy;     //Clear the screen     glClear( GL_COLOR_BUFFER_BIT );     //Start showing the sprite     glTranslatef( sprite_x, sprite_y, 0 );     //Start drawing square     glBegin( GL_QUADS );     glColor4f( 1.0, 1.0, 1.0, 1.0 );     glVertex3f( 0, 0, 0 );     glVertex3f( sprite_width, 0, 0 );     glVertex3f( sprite_width, sprite_height, 0 );     glVertex3f( 0, sprite_height, 0 );     glEnd();     //Reset     glLoadIdentity();     //Update screen     SDL_GL_SwapBuffers();     //Keep frame rate constant     const int ticks_elapsed = static_cast<int>(timer.elapsed() * 1000.0);     if (timer.elapsed() < ticks_per_second)     {       SDL_Delay( ticks_per_second - ticks_elapsed );     }   } }