由于《OpenGL ES 2.0 Programming Guide》原书并没有提供第12章的示例代码，书上的代码也只提到关键的步骤，而网上大多是Android/iOS版本的示例，C/C++的大都基于OpenGL或OpenGL ES 3.0，为了加深理解，遂自己实现了一份C语言版本的，希望能够帮助到同样喜欢OpenGL ES 2.0的同学。
废话不多说，直接上代码：
#include <stdlib.h> #include <stdio.h> #include "esUtil.h" #define SIZE 512 typedef struct { GLuint programFBOObject; GLuint programObject; GLuint frameBuffer; GLuint texture; GLuint depthTexture; GLint positionFBOLoc; GLint mvpFBOLoc; GLint positionLoc; GLint mvpLoc; GLint texcoordLoc; GLint samplerLoc; GLfloat *vertices; GLfloat *texcoords; GLuint *indices; int numIndices; GLfloat angle; ESMatrix mvpMatrix; } UserData; int initFBO(ESContext *esContext, GLint width, GLint height) { GLenum status; //GLint maxRenderbufferSize; UserData *userData = (UserData *)esContext->userData; //glGetIntegerv(GL_MAX_RENDERBUFFER_SIZE, &maxRenderbufferSize); check if GL_MAX_RENDERBUFFER_SIZE is >= texWidth and texHeight //if ((maxRenderbufferSize <= width) || (maxRenderbufferSize <= height)) //{ // // cannot use framebuffer objects as we need to create // // a depth buffer as a renderbuffer object // printf("Cannot use framebuffer objects!\n"); // exit(EXIT_FAILURE); // return FALSE; //} // generate the framebuffer glGenFramebuffers(1, &userData->frameBuffer); // Depth Texture glGenTextures(1, &userData->depthTexture); glBindTexture(GL_TEXTURE_2D, userData->depthTexture); glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, width, height, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_SHORT, NULL); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST ); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST ); // Color Texture glGenTextures(1, &userData->texture); glBindTexture(GL_TEXTURE_2D, userData->texture); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_SHORT_5_6_5, NULL); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); //glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); //glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST ); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST ); // bind the framebuffer glBindFramebuffer(GL_FRAMEBUFFER, userData->frameBuffer); // specify texture as color attachment glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, userData->texture, 0); // ☆specify depth_texture as depth attachment glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, userData->depthTexture, 0); // check for framebuffer complete status = glCheckFramebufferStatus(GL_FRAMEBUFFER); if (status != GL_FRAMEBUFFER_COMPLETE) { printf("Framebuffer object is not complete!\n"); exit(EXIT_FAILURE); return FALSE; } //glBindFramebuffer(GL_FRAMEBUFFER, 0); return TRUE; } int InitFBOShader(ESContext *esContext) { UserData *userData = (UserData *)esContext->userData; const char vShaderStr[] = "uniform mat4 u_mvpMatrix; \n" "attribute vec4 a_position; \n" "void main() \n" "{ \n" " gl_Position = u_mvpMatrix * a_position; \n" "} \n"; const char fShaderStr[] = "precision mediump float; \n" "void main() \n" "{ \n" " gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); \n" "} \n"; userData->programFBOObject = esLoadProgram(vShaderStr, fShaderStr); if (!userData->programFBOObject) return FALSE; // Bind vPosition to attribute 0 //glBindAttribLocation(userData->programFBOObject, 0, "a_position"); userData->positionFBOLoc = glGetAttribLocation ( userData->programFBOObject, "a_position" ); userData->mvpFBOLoc = glGetUniformLocation( userData->programFBOObject, "u_mvpMatrix" ); return TRUE; } int initShader(ESContext *esContext) { UserData *userData = (UserData *)esContext->userData; const char vShaderStr[] = "uniform mat4 u_mvpMatrix; \n" "attribute vec4 a_position; \n" "attribute vec2 a_texCoord; \n" "varying vec2 v_texCoord; \n" "void main() \n" "{ \n" " gl_Position = u_mvpMatrix * a_position; \n" " v_texCoord = a_texCoord; \n" "} \n"; const char fShaderStr[] = "precision mediump float; \n" "varying vec2 v_texCoord; \n" "uniform sampler2D s_texture; \n" "void main() \n" "{ \n" " vec4 color = texture2D(s_texture, v_texCoord); \n" " gl_FragColor = color; \n" "} \n"; // Load the shaders and get a linked program object userData->programObject = esLoadProgram ( vShaderStr, fShaderStr ); // Get the attribute locations userData->positionLoc = glGetAttribLocation ( userData->programObject, "a_position" ); // Get the uniform locations userData->mvpLoc = glGetUniformLocation( userData->programObject, "u_mvpMatrix" ); // Get the texture attribute locations userData->texcoordLoc = glGetAttribLocation(userData->programObject, "a_texCoord"); userData->samplerLoc = glGetUniformLocation(userData->programObject, "s_texture"); return TRUE; } int Init(ESContext *esContext) { UserData *userData = (UserData *)esContext->userData; if (!InitFBOShader(esContext)) { printf("initFBOShader exception ! \n"); return FALSE; } if (!initShader(esContext)) { printf("initShader exception ! \n"); return FALSE; } initFBO(esContext, SIZE, SIZE); // Generate the vertex data userData->numIndices = esGenCube( 1.0, &userData->vertices, NULL, &userData->texcoords, &userData->indices ); // Starting rotation angle for the cube userData->angle = 45.0f; glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f ); glClearDepthf( 1.0f ); glEnable(GL_DEPTH_TEST); glEnable(GL_CULL_FACE); return TRUE; } // Update the mvp matrix void Update(ESContext *esContext, float deltaTime) { UserData *userData = (UserData*) esContext->userData; ESMatrix perspective; ESMatrix modelview; float aspect; // Compute a rotation angle based on time to rotate the cube userData->angle += ( deltaTime * 40.0f ); if( userData->angle >= 360.0f ) userData->angle -= 360.0f; // Compute the window aspect ratio aspect = (GLfloat) esContext->width / (GLfloat) esContext->height; // Generate a perspective matrix with a 60 degree FOV esMatrixLoadIdentity( &perspective ); esPerspective( &perspective, 60.0f, aspect, 1.0f, 20.0f ); // Generate a model view matrix to rotate/translate the cube esMatrixLoadIdentity( &modelview ); // Translate away from the viewer esTranslate( &modelview, 0.0, 0.0, -2.0 ); // Rotate the cube esRotate( &modelview, userData->angle, 1.0, 0.0, 1.0 ); // Compute the final MVP by multiplying the // modevleiw and perspective matrices together esMatrixMultiply( &userData->mvpMatrix, &modelview, &perspective ); } void DrawToFBO(ESContext *esContext) { UserData *userData = (UserData *)esContext->userData; glBindFramebuffer(GL_FRAMEBUFFER, userData->frameBuffer); // Set the viewport glViewport ( 0, 0, esContext->width, esContext->height ); // Clear the color buffer glClearColor ( 1.0f, 1.0f, 1.0f, 1.0f ); glClear ( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Use the program object glUseProgram ( userData->programFBOObject ); // ----------------------------------------------------------- // Load the vertex position glVertexAttribPointer ( userData->positionFBOLoc, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), userData->vertices ); glEnableVertexAttribArray ( userData->positionFBOLoc ); // ----------------------------------------------------------- // Load the MVP matrix glUniformMatrix4fv( userData->mvpFBOLoc, 1, GL_FALSE, (GLfloat*) &userData->mvpMatrix.m[0][0] ); // ----------------------------------------------------------- // Draw the cube glDrawElements ( GL_TRIANGLES, userData->numIndices, GL_UNSIGNED_INT, userData->indices ); } void Draw(ESContext *esContext) { UserData *userData = (UserData *)esContext->userData; DrawToFBO(esContext); glBindFramebuffer(GL_FRAMEBUFFER, 0); // Set the viewport glViewport ( 0, 0, esContext->width, esContext->height ); // Clear the color buffer glClearColor (0.0f, 0.0f, 0.0f, 0.0f); glClear ( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Use the program object glUseProgram ( userData->programObject ); // ----------------------------------------------------------- // Load the vertex position glVertexAttribPointer ( userData->positionLoc, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), userData->vertices ); glEnableVertexAttribArray ( userData->positionLoc ); // ----------------------------------------------------------- // Load the texture coordinate glVertexAttribPointer(userData->texcoordLoc, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(GLfloat), userData->texcoords); glEnableVertexAttribArray(userData->texcoordLoc); // ----------------------------------------------------------- // Load the MVP matrix glUniformMatrix4fv( userData->mvpLoc, 1, GL_FALSE, (GLfloat*) &userData->mvpMatrix.m[0][0] ); // ----------------------------------------------------------- // Bind the texture unit 0 // Set the sampler texture unit to 0 glActiveTexture(GL_TEXTURE0); // Bind a texturing target.While a texture is bound, GL operations on th // -e target to which it is bound affect the bound texture, and queries // of the target to which it is bound return state from the bound texture //glBindTexture(GL_TEXTURE_2D, userData->texture); glBindTexture(GL_TEXTURE_2D, userData->depthTexture); // ☆ glUniform1i(userData->samplerLoc, 0); // ----------------------------------------------------------- // Draw the cube glDrawElements ( GL_TRIANGLES, userData->numIndices, GL_UNSIGNED_INT, userData->indices ); eglSwapBuffers ( esContext->eglDisplay, esContext->eglSurface ); glBindTexture(GL_TEXTURE_2D, 0); } void ShutDown(ESContext *esContext) { UserData *userData = (UserData *)esContext->userData; if ( userData->vertices != NULL ) { free ( userData->vertices ); } if ( userData->texcoords != NULL ) { free ( userData->texcoords ); } if ( userData->indices != NULL ) { free ( userData->indices ); } // Delete program object glDeleteProgram (userData->programObject); glDeleteProgram(userData->programFBOObject); // Delete texture glDeleteTextures(1, &userData->texture); glDeleteTextures(1, &userData->depthTexture); glDeleteFramebuffers(1, &userData->frameBuffer); } int main ( int argc, char *argv[] ) { ESContext esContext; UserData userData; esInitContext ( &esContext ); esContext.userData = &userData; esCreateWindow ( &esContext, "Simple FBO", SIZE, SIZE, ES_WINDOW_RGB ); if ( !Init ( &esContext ) ) return 0; esRegisterDrawFunc ( &esContext, Draw ); esRegisterUpdateFunc ( &esContext, Update ); esMainLoop ( &esContext ); ShutDown ( &esContext ); }
效果图：
