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：

1. /*****************************************************************************
2. Copyright: 2012, ustc All rights reserved.
3. contact:[email protected]
4. File name: main.c
5. Description:using opengl in SDL.
6. Author:Silang Quan
7. Version: 1.0
8. Date: 2012.12.01
9. *****************************************************************************/
10. #include <SDL/SDL.h>
11. #include <GL/gl.h>
12. #include <GL/glu.h>
13. #include <stdio.h>
14. #include <stdlib.h>
15. SDL_Surface *screen;
16. void quit( int code )
17. {
18. SDL_Quit( );
19. /* Exit program. */
20. exit( code );
21. }
22. void handleKeyEvent( SDL_keysym* keysym )
23. {
24. switch( keysym->sym )
25. {
26. case SDLK_ESCAPE:
27. quit( 0 );
28. break;
29. case SDLK_SPACE:
30. break;
31. default:
32. break;
33. }
34. }
35. void resizeGL(int width,int height)
36. {
37. if ( height == 0 )
38. {
39. height = 1;
40. }
41. //Reset View
42. glViewport( 0, 0, (GLint)width, (GLint)height );
43. //Choose the Matrix mode
44. glMatrixMode( GL_PROJECTION );
45. //reset projection
46. glLoadIdentity();
47. //set perspection
48. gluPerspective( 45.0, (GLfloat)width/(GLfloat)height, 0.1, 100.0 );
49. //choose Matrix mode
50. glMatrixMode( GL_MODELVIEW );
51. glLoadIdentity();
52. }
53. void handleEvents()
54. {
55. // Our SDL event placeholder.
56. SDL_Event event;
57. //Grab all the events off the queue.
58. while( SDL_PollEvent( &event ) ) {
59. switch( event.type ) {
60. case SDL_KEYDOWN:
61. // Handle key Event
62. handleKeyEvent( &event.key.keysym );
63. break;
64. case SDL_QUIT:
65. // Handle quit requests (like Ctrl-c).
66. quit( 0 );
67. break;
68. case SDL_VIDEORESIZE:
69. //Handle resize event
70. screen = SDL_SetVideoMode(event.resize.w, event.resize.h, 16,
71. SDL_OPENGL|SDL_RESIZABLE);
72. if ( screen )
73. {
74. resizeGL(screen->w, screen->h);
75. }
76. break;
77. }
78. }
79. }
81. void initSDL(int width,int height,int bpp,int flags)
82. {
83. // First, initialize SDL's video subsystem.
84. if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
85. {
86. fprintf( stderr, "Video initialization failed: %s\n",
87. SDL_GetError( ) );
88. quit( 1 );
89. }
90. atexit(SDL_Quit);
91. //Set some Attribute of OpenGL in SDL
92. SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
93. SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
94. SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
95. SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
96. SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
98. //Set the video mode
99. screen= SDL_SetVideoMode( width, height, bpp,flags);
100. if(!screen )
101. {
102. fprintf( stderr, "Video mode set failed: %s\n",SDL_GetError( ) );
103. quit( 1 );
104. }
105. resizeGL(screen->w, screen->h);
106. //Set caption
107. SDL_WM_SetCaption( "OpenGL Test", NULL );
108. }
109. void renderGL()
110. {
111. // Clear the color and depth buffers.
112. glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
113. // We don't want to modify the projection matrix. */
114. glMatrixMode( GL_MODELVIEW );
115. glLoadIdentity( );
116. // Move down the z-axis.
117. glTranslatef( 0.0, 0.0, -5.0 );
118. //Draw a square
119. glBegin(GL_QUADS);
120. glColor3f(1.0f,0.0f,0.0f);
121. glVertex3f(-1.0f , -1.0f , 1.0f );
122. glColor3f(0.0f,1.0f,0.0f);
123. glVertex3f( 1.0f , -1.0f , 1.0f );
124. glColor3f(0.0f,0.0f,1.0f);
125. glVertex3f( 1.0f , 1.0f , 1.0f );
126. glColor3f(1.0f,1.0f,0.0f);
127. glVertex3f(-1.0f , 1.0f , 1.0f );
128. glEnd();
129. SDL_GL_SwapBuffers( );
130. }
131. void initGL( int width, int height )
132. {
133. float ratio = (float) width / (float) height;
134. // Our shading model--Gouraud (smooth).
135. glShadeModel( GL_SMOOTH );
136. // Set the clear color.
137. glClearColor( 0, 0, 0, 0 );
138. // Setup our viewport.
139. glViewport( 0, 0, width, height );
140. //Change to the projection matrix and set our viewing volume.
141. glMatrixMode( GL_PROJECTION );
142. glLoadIdentity();
143. gluPerspective( 60.0, ratio, 1.0, 100.0 );
144. }
145. int main( int argc, char* argv[] )
146. {
148. // Dimensions of our window.
149. int width = 640;
150. int height = 480;
151. // Color depth in bits of our window.
152. int bpp = 32;
153. int flags= SDL_OPENGL|SDL_RESIZABLE;
154. //Set the SDL
155. initSDL(width, height, bpp,flags);
156. //Set the OpenGL
157. initGL( width, height );
159. //main loop
160. while(true)
161. {
162. /* Process incoming events. */
163. handleEvents( );
164. /* Draw the screen. */
165. renderGL( );
166. }
167. return 0;
168. }