《OpenGL ES 2.0 Programming Guide》第9章 “最简单的本地纹理显示”示例代码【C语言版】

由于《OpenGL ES 2.0 Programming Guide》原书第9章并没有提供本地纹理加载的示例，都是程序生成的，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 "esUtil.h"

typedef struct
{
// Handle to a program object
GLuint programObject;

// Attribute locations
GLint positionLoc;
GLint texCoordLoc;

// Sampler location
GLint samplerLoc;

// Texture handle
GLuint textureId;

} UserData;

///
// Load texture from disk
//
GLuint LoadTexture ( char *fileName )
{
int width, height;

char *buffer = esLoadTGA ( fileName, &width, &height );
GLuint texId;

if ( buffer == NULL )
{
esLogMessage ( "Error loading (%s) image.\n", fileName );
return 0;
}

glGenTextures ( 1, &texId );
glBindTexture ( GL_TEXTURE_2D, texId );

glTexImage2D ( GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, buffer );
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );

free ( buffer );

return texId;
}

///
// Initialize the shader and program object
//
int Init ( ESContext *esContext )
{
char *fileName = "D:/Projects/Visual Studio 2012/OpenGL_Demo/opengles-book-samples-master/Windows/Chapter_9/Simple_Texture2D/Fieldstone.tga";

UserData *userData = esContext->userData;
GLbyte vShaderStr[] =
"attribute vec4 a_position; \n"
"attribute vec2 a_texCoord; \n"
"varying vec2 v_texCoord; \n"
"void main() \n"
"{ \n"
" gl_Position = a_position; \n"
" v_texCoord = a_texCoord; \n"
"} \n";

GLbyte fShaderStr[] =
"precision mediump float; \n"
"varying vec2 v_texCoord; \n"
"uniform sampler2D s_texture; \n"
"void main() \n"
"{ \n"
" gl_FragColor = texture2D( s_texture, v_texCoord );\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" );
userData->texCoordLoc = glGetAttribLocation ( userData->programObject, "a_texCoord" );

// Get the sampler location
userData->samplerLoc = glGetUniformLocation ( userData->programObject, "s_texture" );

// Load the texture
//userData->textureId = CreateSimpleTexture2D ();
userData->textureId = LoadTexture(fileName);

glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f );
return TRUE;
}

///
// Draw a triangle using the shader pair created in Init()
//
void Draw ( ESContext *esContext )
{
UserData *userData = esContext->userData;
GLfloat vVertices[] = { -0.5f, 0.5f, 0.0f, // Position 0
0.0f, 0.0f, // TexCoord 0
-0.5f, -0.5f, 0.0f, // Position 1
0.0f, 1.0f, // TexCoord 1
0.5f, -0.5f, 0.0f, // Position 2
1.0f, 1.0f, // TexCoord 2
0.5f, 0.5f, 0.0f, // Position 3
1.0f, 0.0f // TexCoord 3
};
GLushort indices[] = { 0, 1, 2, 0, 2, 3 };

// Set the viewport
glViewport ( 0, 0, esContext->width, esContext->height );

// Clear the color buffer
glClear ( GL_COLOR_BUFFER_BIT );

// Use the program object
glUseProgram ( userData->programObject );

// Load the vertex position
glVertexAttribPointer ( userData->positionLoc, 3, GL_FLOAT,
GL_FALSE, 5 * sizeof(GLfloat), vVertices );
// Load the texture coordinate
glVertexAttribPointer ( userData->texCoordLoc, 2, GL_FLOAT,
GL_FALSE, 5 * sizeof(GLfloat), &vVertices[3] );

glEnableVertexAttribArray ( userData->positionLoc );
glEnableVertexAttribArray ( userData->texCoordLoc );

// Bind the texture
glActiveTexture ( GL_TEXTURE0 );
glBindTexture ( GL_TEXTURE_2D, userData->textureId );

// Set the sampler texture unit to 0
glUniform1i ( userData->samplerLoc, 0 );

glDrawElements ( GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, indices );

eglSwapBuffers ( esContext->eglDisplay, esContext->eglSurface );
}

///
// Cleanup
//
void ShutDown ( ESContext *esContext )
{
UserData *userData = esContext->userData;

// Delete texture object
glDeleteTextures ( 1, &userData->textureId );

// Delete program object
glDeleteProgram ( userData->programObject );
}

int main ( int argc, char *argv[] )
{
ESContext esContext;
UserData userData;

esInitContext ( &esContext );
esContext.userData = &userData;

esCreateWindow ( &esContext, "Simple Texture 2D", 512, 512, ES_WINDOW_RGB );

if ( !Init ( &esContext ) )
return 0;

esRegisterDrawFunc ( &esContext, Draw );

esMainLoop ( &esContext );

ShutDown ( &esContext );
}


效果如图