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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
//
// Hello_Triangle.c
//
// This is a simple example that draws a single triangle with
// a minimal vertex/fragment shader. The purpose of this
// example is to demonstrate the basic concepts of
// OpenGL ES 2.0 rendering.
#include <stdlib.h>
#include "esUtil.h"
typedef struct
{
// Handle to a program object
GLuint programObject;
} UserData;
///
// Create a shader object, load the shader source, and
// compile the shader.
//
GLuint LoadShader ( GLenum type, const char *shaderSrc )
{
GLuint shader;
GLint compiled;
// Create the shader object
shader = glCreateShader ( type );
if ( shader == 0 )
return 0;
// Load the shader source
glShaderSource ( shader, 1, &shaderSrc, NULL );
// Compile the shader
glCompileShader ( shader );
// Check the compile status
glGetShaderiv ( shader, GL_COMPILE_STATUS, &compiled );
if ( !compiled )
{
GLint infoLen = 0;
glGetShaderiv ( shader, GL_INFO_LOG_LENGTH, &infoLen );
if ( infoLen > 1 )
{
char* infoLog = malloc (sizeof(char) * infoLen );
glGetShaderInfoLog ( shader, infoLen, NULL, infoLog );
esLogMessage ( "Error compiling shader:\n%s\n", infoLog );
free ( infoLog );
}
glDeleteShader ( shader );
return 0;
}
return shader;
}
///
// Initialize the shader and program object
//
int Init ( ESContext *esContext )
{
esContext->userData = malloc(sizeof(UserData));
UserData *userData = esContext->userData;
GLbyte vShaderStr[] =
"attribute vec4 vPosition; \n"
"void main() \n"
"{ \n"
" gl_Position = vPosition; \n"
"} \n";
GLbyte fShaderStr[] =
"precision mediump float;\n"\
"void main() \n"
"{ \n"
" gl_FragColor = vec4 ( 1.0, 0.0, 0.0, 1.0 );\n"
"} \n";
GLuint vertexShader;
GLuint fragmentShader;
GLuint programObject;
GLint linked;
// Load the vertex/fragment shaders
vertexShader = LoadShader ( GL_VERTEX_SHADER, vShaderStr );
fragmentShader = LoadShader ( GL_FRAGMENT_SHADER, fShaderStr );
// Create the program object
programObject = glCreateProgram ( );
if ( programObject == 0 )
return 0;
glAttachShader ( programObject, vertexShader );
glAttachShader ( programObject, fragmentShader );
// Bind vPosition to attribute 0
glBindAttribLocation ( programObject, 0, "vPosition" );
// Link the program
glLinkProgram ( programObject );
// Check the link status
glGetProgramiv ( programObject, GL_LINK_STATUS, &linked );
if ( !linked )
{
GLint infoLen = 0;
glGetProgramiv ( programObject, GL_INFO_LOG_LENGTH, &infoLen );
if ( infoLen > 1 )
{
char* infoLog = malloc (sizeof(char) * infoLen );
glGetProgramInfoLog ( programObject, infoLen, NULL, infoLog );
esLogMessage ( "Error linking program:\n%s\n", infoLog );
free ( infoLog );
}
glDeleteProgram ( programObject );
return GL_FALSE;
}
// Store the program object
userData->programObject = programObject;
glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f );
return GL_TRUE;
}
///
// Draw a triangle using the shader pair created in Init()
//
void Draw ( ESContext *esContext )
{
UserData *userData = esContext->userData;
GLfloat vVertices[] = { 0.0f, 0.5f, 0.0f,
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f };
// No clientside arrays, so do this in a webgl-friendly manner
GLuint vertexPosObject;
glGenBuffers(1, &vertexPosObject);
glBindBuffer(GL_ARRAY_BUFFER, vertexPosObject);
glBufferData(GL_ARRAY_BUFFER, 9*4, vVertices, GL_STATIC_DRAW);
// 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 data
glBindBuffer(GL_ARRAY_BUFFER, vertexPosObject);
glVertexAttribPointer(0 /* ? */, 3, GL_FLOAT, 0, 0, 0);
glEnableVertexAttribArray(0);
glDrawArrays ( GL_TRIANGLES, 0, 3 );
}
int main ( int argc, char *argv[] )
{
ESContext esContext;
UserData userData;
esInitContext ( &esContext );
esContext.userData = &userData;
esCreateWindow ( &esContext, "Hello Triangle", 320, 240, ES_WINDOW_RGB );
if ( !Init ( &esContext ) )
return 0;
esRegisterDrawFunc ( &esContext, Draw );
esMainLoop ( &esContext );
}
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