Added simple vertex shader demo....

third_party/gles2_book/Chapter_8/Simple_VertexShader/Simple_VertexShader.c

 //
 // 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_VertexShader.c
 //
 //    This is a simple example that draws a rotating cube in perspective
 //    using a vertex shader to transform the object
 //
 
 #include "Simple_VertexShader.h"
 #include <stdlib.h>
 
 ///
 // Initialize the shader and program object
 //
 int svsInit ( ESContext *esContext )
 {
    SVSUserData *userData = esContext->userData;
+   int numVertices = 24;
+   GLfloat *vertices = NULL;
+   GLushort *indices = NULL;
+
    GLbyte vShaderStr[] =  
       "uniform mat4 u_mvpMatrix;                   \n"
       "attribute vec4 a_position;                  \n"
       "void main()                                 \n"
       "{                                           \n"
       "   gl_Position = u_mvpMatrix * a_position;  \n"
       "}                                           \n";
    
    // TODO(alokp): Shaders containing "precision" do not compile.
    GLbyte fShaderStr[] =  
       "//precision mediump float;                            \n"
       "void main()                                         \n"
       "{                                                   \n"
       "  gl_FragColor = vec4( 1.0, 0.0, 0.0, 1.0 );        \n"
       "}                                                   \n";
 
    // Load the shaders and get a linked program object
    userData->programObject = esLoadProgram ( vShaderStr, fShaderStr );
+   if ( userData->programObject == 0 ) return FALSE;
 
    // Get the attribute locations
    userData->positionLoc = glGetAttribLocation ( userData->programObject, "a_position" );
 
    // Get the uniform locations
    userData->mvpLoc = glGetUniformLocation( userData->programObject, "u_mvpMatrix" );
    
    // Generate the vertex data
-   userData->numIndices = esGenCube( 1.0, &userData->vertices,
-                                     NULL, NULL, &userData->indices );
-   
+   userData->numIndices = esGenCube( 1.0, &vertices, NULL, NULL, &indices );
+   glGenBuffers ( 2, userData->vboIds );
+   glBindBuffer ( GL_ARRAY_BUFFER, userData->vboIds[0] );
+   glBufferData ( GL_ARRAY_BUFFER, 3 * numVertices * sizeof(GLfloat),
+                  vertices, GL_STATIC_DRAW );
+   glBindBuffer ( GL_ELEMENT_ARRAY_BUFFER, userData->vboIds[1] );
+   glBufferData ( GL_ELEMENT_ARRAY_BUFFER, userData->numIndices * sizeof(GL_UNSIGNED_SHORT),
+                  indices, GL_STATIC_DRAW );
+   if ( vertices != NULL ) free ( vertices );
+   if ( indices != NULL ) free ( indices );
+
    // Starting rotation angle for the cube
    userData->angle = 45.0f;
 
    glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f );
    return TRUE;
 }
 
 ///
 // Update MVP matrix based on time
 //
@@ skipping 33 matching lines @@
 ///
 // Draw a triangle using the shader pair created in Init()
 //
 void svsDraw ( ESContext *esContext )
 {
    SVSUserData *userData = esContext->userData;
    
    // 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
+   glEnableVertexAttribArray ( userData->positionLoc );

[greggman, 2010/01/13 03:10:43]

Any particular reason you switched the order of these two lines?

[alokp, 2010/01/13 03:52:59]

no particular reason. does it matter?

    glVertexAttribPointer ( userData->positionLoc, 3, GL_FLOAT, 
-                           GL_FALSE, 3 * sizeof(GLfloat), userData->vertices );
-   
-   glEnableVertexAttribArray ( userData->positionLoc );
-   
-   
+                           GL_FALSE, 3 * sizeof(GLfloat), 0 );
+
    // Load the MVP matrix
    glUniformMatrix4fv( userData->mvpLoc, 1, GL_FALSE, (GLfloat*) &userData->mvpMatrix.m[0][0] );
    
    // Draw the cube
-   glDrawElements ( GL_TRIANGLES, userData->numIndices, GL_UNSIGNED_INT, userData->indices );
+   glDrawElements ( GL_TRIANGLES, userData->numIndices, GL_UNSIGNED_SHORT, 0 );
 
    // TODO(alokp): glFlush should not be necessary with SwapBuffers.
    glFlush();
 }
 
 ///
 // Cleanup
 //
 void svsShutDown ( ESContext *esContext )
 {
    SVSUserData *userData = esContext->userData;
 
-   if ( userData->vertices != NULL )
-   {
-      free ( userData->vertices );
-   }
-
-   if ( userData->indices != NULL )
-   {
-      free ( userData->indices );
-   }
+   // Delete program object
+   glDeleteBuffers ( 2, userData->vboIds );
 
    // Delete program object
    glDeleteProgram ( userData->programObject );
 }