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//
// Book: OpenGL(R) ES 2.0 Programming Guide
// Authors: Aaftab Munshi, Dan Ginsburg, Dave Shreiner
// ISBN-10: 0321502795
// ISBN-13: 9780321502797
// Publisher: Addison-Wesley Professional
// URLs: http://safari.informit.com/9780321563835
// http://www.opengles-book.com
//
// Simple_Texture2D.c
//
// This is a simple example that draws a quad with a 2D
// texture image. The purpose of this example is to demonstrate
// the basics of 2D texturing
//
#include <stdlib.h>
#include "esUtil.h"
GLubyte blue=0;
typedef struct
{
// Handle to a program object
GLuint programObject;
// Attribute locations
GLint positionLoc;
GLint texCoordLoc;
// Sampler location
GLint samplerLoc;
// Texture handle
GLuint textureId;
float time;
} UserData;
///
// Create a simple 2x2 texture image with four different colors
//
GLuint CreateSimpleTexture2D( )
{
// Texture object handle
GLuint textureId;
// 2x2 Image, 3 bytes per pixel (R, G, B)
GLubyte pixels[4 * 3] =
{
255, 0, 0, // Red
0, 255, 0, // Green
0, 0, 255, // Blue
255, 255, 0 // Yellow
};
pixels[2] = blue;
if (blue == 255)
blue =0;
blue++;
// Use tightly packed data
glPixelStorei ( GL_UNPACK_ALIGNMENT, 1 );
// Generate a texture object
glGenTextures ( 1, &textureId );
// Bind the texture object
glBindTexture ( GL_TEXTURE_2D, textureId );
// Load the texture
glTexImage2D ( GL_TEXTURE_2D, 0, GL_RGB, 2, 2, 0, GL_RGB, GL_UNSIGNED_BYTE, pixels );
// Set the filtering mode
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
return textureId;
}
///
// Initialize the shader and program object
//
int Init ( ESContext *esContext )
{
esContext->userData = malloc(sizeof(UserData));
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->time = 1.0f;
glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f );
return GL_TRUE;
}
void Update(ESContext *esContext, float deltaTime) {
UserData *userData = esContext ->userData;
glDeleteTextures ( 1, &userData->textureId );
userData->textureId = CreateSimpleTexture2D ();
}
///
// 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 );
}
///
// Cleanup
//
void ShutDown ( ESContext *esContext )
{
UserData *userData = esContext->userData;
// Delete texture object
glDeleteTextures ( 1, &userData->textureId );
// Delete program object
glDeleteProgram ( userData->programObject );
free(esContext->userData);
}
int main ( int argc, char *argv[] )
{
ESContext esContext;
UserData userData;
esInitContext ( &esContext );
esContext.userData = &userData;
esCreateWindow ( &esContext, "Simple Texture 2D", 320, 240, ES_WINDOW_RGB );
if ( !Init ( &esContext ) )
return 0;
esRegisterDrawFunc ( &esContext, Draw );
esRegisterUpdateFunc ( &esContext, Update);
esMainLoop ( &esContext );
ShutDown ( &esContext );
}
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