《OpenGL ES 2.0 Programming Guide》第8章 “最简单的Vertex Buffer Object”示例代码【C语言版】

#include "esUtil.h"
typedef struct
{
  // Handle to a program object
  GLuint programObject;
  GLint positionLoc;
  GLint colorLoc; 
  // VertexBufferObject Ids
  GLuint vboIds[3];
} UserData;
#define VERTEX_POS_SIZE       3 // x, y and z
#define VERTEX_COLOR_SIZE     4 // r, g, b, and a
int Init ( ESContext *esContext )
{
  UserData *userData = esContext->userData;
  const char vShaderStr[] =
    "attribute vec3 a_position;         \n"
    "attribute vec4 a_color;          \n"
    "varying vec4 v_color;            \n"
    "void main()                \n"
    "{                      \n"
    "    v_color = a_color;           \n"
    "    gl_Position = vec4(a_position, 1.0); \n"
    "}                      \n";
  const char fShaderStr[] =
    "precision mediump float;           \n"
    "varying vec4 v_color;              \n"
    "void main()                  \n"
    "{                        \n"
    "    gl_FragColor = v_color;          \n"
    "}                        \n" ;
  GLuint programObject;
  // Create the program object
  programObject = esLoadProgram ( vShaderStr, fShaderStr );
  if ( programObject == 0 )
  {
    return GL_FALSE;
  }
  // Store the program object
  userData->programObject = programObject;
  userData->vboIds[0] = 0;// pos
  userData->vboIds[1] = 0;// color
  userData->vboIds[2] = 0;// index
  userData->positionLoc = glGetAttribLocation(userData->programObject, "a_position");
  userData->colorLoc = glGetAttribLocation(userData->programObject, "a_color");
  glClearColor ( 1.0f, 1.0f, 1.0f, 0.0f );
  return GL_TRUE;
}
void DrawPrimitiveWithVBOs ( ESContext *esContext,
        GLint numVertices, GLfloat *vertexPosBuf, GLfloat *vertexColorBuf,
        GLint *vtxStrides, GLint numIndices,
        GLushort *indices )
{
  UserData *userData = esContext->userData;
  // vboIds[0] - used to store vertex position
  // vboIds[1] - used to store vertex color
  // vboIds[2] - used to store element indices
  // run only once
  if ( userData->vboIds[0] == 0 && userData->vboIds[1] == 0 &&
    userData->vboIds[2] == 0 )
  {
    // Only allocate on the first draw
    glGenBuffers ( 3, userData->vboIds );
    glBindBuffer ( GL_ARRAY_BUFFER, userData->vboIds[0] );
    glBufferData ( GL_ARRAY_BUFFER, vtxStrides[0] * numVertices,
      vertexPosBuf, GL_STATIC_DRAW );
    glBindBuffer ( GL_ARRAY_BUFFER, userData->vboIds[1] );
    glBufferData ( GL_ARRAY_BUFFER, vtxStrides[1] * numVertices,
      vertexColorBuf, GL_STATIC_DRAW );
    glBindBuffer ( GL_ELEMENT_ARRAY_BUFFER, userData->vboIds[2] );
    glBufferData ( GL_ELEMENT_ARRAY_BUFFER,
      sizeof ( GLushort ) * numIndices,
      indices, GL_STATIC_DRAW );
  }
  glBindBuffer ( GL_ARRAY_BUFFER, userData->vboIds[0] );
  glVertexAttribPointer ( userData->positionLoc, 
    VERTEX_POS_SIZE,
    GL_FLOAT, GL_FALSE, vtxStrides[0], 0 );
  glEnableVertexAttribArray ( userData->positionLoc );
  glBindBuffer ( GL_ARRAY_BUFFER, userData->vboIds[1] );
  glVertexAttribPointer ( userData->colorLoc,
    VERTEX_COLOR_SIZE,
    GL_FLOAT, GL_FALSE, vtxStrides[1], 0 );
  glEnableVertexAttribArray ( userData->colorLoc );
  glBindBuffer ( GL_ELEMENT_ARRAY_BUFFER, userData->vboIds[2] );
  glDrawElements ( GL_TRIANGLES, numIndices,
    GL_UNSIGNED_SHORT, 0 );
  eglSwapBuffers ( esContext->eglDisplay, esContext->eglSurface );  // ☆
  // ---------------------------------------------------
  glDisableVertexAttribArray ( userData->positionLoc );
  glDisableVertexAttribArray ( userData->colorLoc );
  glBindBuffer ( GL_ARRAY_BUFFER, 0 );
  glBindBuffer ( GL_ELEMENT_ARRAY_BUFFER, 0 );
}
void Draw ( ESContext *esContext )
{
  UserData *userData = esContext->userData;
  // 3 vertices, with (x,y,z) ,(r, g, b, a) per-vertex
  GLfloat vertexPos[3 * VERTEX_POS_SIZE] =
  {
    0.0f,  0.5f, 0.0f,         // v0
    -0.5f, -0.5f, 0.0f,        // v1
    0.5f, -0.5f, 0.0f          // v2
  };
  GLfloat color[4 * VERTEX_COLOR_SIZE] =
  {
    1.0f, 0.0f, 0.0f, 1.0f,   // c0
    0.0f, 1.0f, 0.0f, 1.0f,   // c1
    0.0f, 0.0f, 1.0f, 1.0f    // c2
  };
  GLint vtxStrides[2] =
  {
    VERTEX_POS_SIZE * sizeof ( GLfloat ),
    VERTEX_COLOR_SIZE * sizeof ( GLfloat )
  };
  // Index buffer data
  GLushort indices[3] = { 0, 1, 2 };
  //GLfloat *vtxBuf[2] = { vertexPos, color };
  glViewport ( 0, 0, esContext->width, esContext->height );
  glClear ( GL_COLOR_BUFFER_BIT );
  glUseProgram ( userData->programObject );
  DrawPrimitiveWithVBOs ( esContext, 3, vertexPos, color,
    vtxStrides, 3, indices );
}
void ShutDown ( ESContext *esContext )
{
  UserData *userData = esContext->userData;
  glDeleteProgram ( userData->programObject );
  glDeleteBuffers ( 3, userData->vboIds );
}
int main ( int argc, char *argv[] )
{
  ESContext esContext;
  UserData  userData;
  esInitContext ( &esContext );
  esContext.userData = &userData;
  esCreateWindow ( &esContext, "SimpleVBO", 320, 240, ES_WINDOW_RGB );
  if ( !Init ( &esContext ) )
  {
    return GL_FALSE;
  }
  esRegisterDrawFunc ( &esContext, Draw );
  esMainLoop ( &esContext );
  ShutDown ( &esContext );
  return GL_TRUE;
}