SDL入门学习续-在SDL中使用OpenGL

       配置好SDL之后，就想在SDL中使用openGL，原以为会像在GLFW中那样简单的，实际上确花费了一整个下午不断查看文档，实例才搞定问题。

总结如下：

1）SDL对OpenGL进行了部分的封装，一些OpenGL的函数需要用SDL来实现，而不是像GLFW中那样直接用；

2）SDL的事件机制花费了一些时间来理解；

3）在处理OpenGL窗口大小变化的时候，需要先调用SDL_SetVideoMode才可以得到正确结果。

最终基本实现了一个opengl的小型框架，包括一些简单的事件处理。

代码：

/*****************************************************************************
Copyright: 2012, ustc All rights reserved.
contact:[email protected]
File name: main.c
Description:using opengl in SDL.
Author:Silang Quan
Version: 1.0
Date: 2012.12.01
*****************************************************************************/
#include <SDL/SDL.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <stdio.h>
#include <stdlib.h>
const int SCREEN_WIDTH = 800;
const int SCREEN_HEIGHT =800;
const int SCREEN_BPP = 32;
SDL_Surface *screen;
//Whether the window is windowed or not
bool windowed;
//Whether the window is fine
bool windowOK;
void quit( int code )
{
    SDL_Quit( );
    /* Exit program. */
    exit( code );
}
void toggle_fullscreen()
{
	//If the screen is windowed
	if( windowed == true )
	{
		//Set the screen to fullscreen
		screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_OPENGL|SDL_RESIZABLE| SDL_FULLSCREEN );

		//If there's an error
		if( screen == NULL )
		{
			windowOK = false;
			return;
		}

		//Set the window state flag
		windowed = false;
	}
	//If the screen is fullscreen
	else if( windowed == false )
	{
		//Window the screen
		screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_OPENGL|SDL_RESIZABLE );

		//If there's an error
		if( screen == NULL )
		{
			windowOK = false;
			return;
		}

		//Set the window state flag
		windowed = true;
	}
}
void handleKeyEvent( SDL_keysym* keysym )
{
    switch( keysym->sym )
	{
    case SDLK_ESCAPE:
        quit( 0 );
        break;
    case SDLK_SPACE:
        break;
    case SDLK_F1:
		toggle_fullscreen();
		break;
    default:
        break;
    }
}
void resizeGL(int width,int height)
{
    if ( height == 0 )
    {
        height = 1;
    }
    //Reset View
    glViewport( 0, 0, (GLint)width, (GLint)height );
    //Choose the Matrix mode
    glMatrixMode( GL_PROJECTION );
    //reset projection
    glLoadIdentity();
    //set perspection
    gluPerspective( 45.0, (GLfloat)width/(GLfloat)height, 0.1, 100.0 );
    //choose Matrix mode
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();
}
void handleEvents()
{
    // Our SDL event placeholder.
    SDL_Event event;
    //Grab all the events off the queue.
    while( SDL_PollEvent( &event ) ) {
        switch( event.type ) {
        case SDL_KEYDOWN:
            // Handle key Event
            handleKeyEvent( &event.key.keysym );
            break;
        case SDL_QUIT:
            // Handle quit requests (like Ctrl-c).
            quit( 0 );
            break;
        case SDL_VIDEORESIZE:
			//Handle resize event
            screen = SDL_SetVideoMode(event.resize.w, event.resize.h, 16,
                                      SDL_OPENGL|SDL_RESIZABLE);
            if ( screen )
            {
                resizeGL(screen->w, screen->h);
            }
            break;
        }
    }
}

void initSDL(int width,int height,int bpp,int flags)
{
    // First, initialize SDL's video subsystem.
    if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
    {
        fprintf( stderr, "Video initialization failed: %s\n",
                 SDL_GetError( ) );
        quit( 1 );
    }
    atexit(SDL_Quit);
	//Set some Attribute of OpenGL in SDL
    SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
    SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );

    //Set the video mode
    screen= SDL_SetVideoMode( width, height, bpp,flags);
    if(!screen )
    {
        fprintf( stderr, "Video mode set failed: %s\n",SDL_GetError( ) );
        quit( 1 );
    windowed=false;
	}
	else windowed=true;
    resizeGL(screen->w, screen->h);
    //Set caption
    SDL_WM_SetCaption( "OpenGL Test", NULL );
}
void renderGL()
{
    // Clear the color and depth buffers.
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
    // We don't want to modify the projection matrix. */
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity( );
    // Move down the z-axis.
    glTranslatef( 0.0, 0.0, -5.0 );
	//Draw a square
    glBegin(GL_QUADS);
    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(-1.0f  , -1.0f  ,  1.0f  );
    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f( 1.0f  , -1.0f  ,  1.0f  );
    glColor3f(0.0f,0.0f,1.0f);
    glVertex3f( 1.0f  ,  1.0f  ,  1.0f  );
    glColor3f(1.0f,1.0f,0.0f);
    glVertex3f(-1.0f  ,  1.0f  ,  1.0f  );
    glEnd();
    SDL_GL_SwapBuffers( );
}
void initGL( int width, int height )
{
    float ratio = (float) width / (float) height;
    // Our shading model--Gouraud (smooth).
    glShadeModel( GL_SMOOTH );
    // Set the clear color.
    glClearColor( 0, 0, 0, 0 );
    // Setup our viewport.
    glViewport( 0, 0, width, height );
    //Change to the projection matrix and set our viewing volume.
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    gluPerspective( 60.0, ratio, 1.0, 100.0 );
}
int main( int argc, char* argv[] )
{

	// Color depth in bits of our window.
	int flags= SDL_OPENGL|SDL_RESIZABLE;
	//Set the SDL
	initSDL(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP,flags);
	//Set the OpenGL
	initGL(SCREEN_WIDTH, SCREEN_HEIGHT );

    //main loop
    while(true)
	{
        /* Process incoming events. */
        handleEvents( );
        /* Draw the screen. */
        renderGL( );
    }
    return 0;
}

编译命令：

 g++ main.c -o mian -lSDL -lglut -lGLU

#in opensuse
g++ main.c -o main -lSDL -lGL -lGLU

SDLOpenGLFramework

这里给一个C++写的OpenGL编程框架。

https://github.com/SilangQuan/SDLOpenGLFramework

SDL英文教程-http://lazyfoo.net/