使用OpenGL的VBO时出现问题

Question

我只是尝试使用VBO渲染第一个红皮书示例(白色Quad).
它适用于立即模式和顶点数组.

但是当使用VBO时,屏幕保持黑色.我想我一定错过了重要的事情.

在里面:

unsigned int bufIds[2];
glGenBuffers( 2, bufIds );
GLfloat vertices[] = {
  0.25, 0.25, 0.0,
  0.75, 0.25, 0.0,
  0.75, 0.75, 0.0,
  0.25, 0.75, 0.0
};
glBindBuffer( GL_ARRAY_BUFFER, bufIds[0] );
glBufferData( GL_ARRAY_BUFFER, 12, vertices, GL_STATIC_DRAW );
glBindBuffer( GL_ARRAY_BUFFER, 0 );

glClearColor( 0, 0, 0, 1 );
glColor3f( 1, 1, 1 );
glOrtho( 0.0, 1.0, 0.0, 1.0, -1.0, 1.0 );

VBO的renderloop(不工作):

glClear( GL_COLOR_BUFFER_BIT );
glEnableClientState( GL_VERTEX_ARRAY );
glBindBuffer( GL_ARRAY_BUFFER, bufIds[0] );
glVertexPointer( 3, GL_FLOAT, 0, 0 );
glDrawArrays( GL_QUADS, 0, 12 );
glBindBuffer( GL_ARRAY_BUFFER, 0 );
glDisableClientState( GL_VERTEX_ARRAY );

顶点数组的renderloop(工作):

glClear( GL_COLOR_BUFFER_BIT );
glEnableClientState( GL_VERTEX_ARRAY );
glBindBuffer( GL_ARRAY_BUFFER, 0 );
glVertexPointer( 3, GL_FLOAT, 0, vertices );
glDrawArrays( GL_QUADS, 0, 12 );
glDisableClientState( GL_VERTEX_ARRAY );

Answer 1

我想通过尝试回读缓冲区的内容来解决这个问题:

我需要使用12*sizeof(GLfloat)而不是12来分配缓冲区

glBufferData( GL_ARRAY_BUFFER, 12 * sizeof( GLfloat ), vertices, GL_STATIC_DRAW );

我的回读代码

GLfloat vertices2[12];
glBindBuffer( GL_ARRAY_BUFFER, bufIds[0] );
glGetBufferSubData ( GL_ARRAY_BUFFER, 0, 12 * sizeof( GLfloat ), vertices2 );
glBindBuffer( GL_ARRAY_BUFFER, 0 );

for ( int i = 0; i < 4; i ++ ) {
    LOG_DEBUG << "point " << i << ": " << vertices2[ i * 3 + 0 ] << " / " << vertices2[ i * 3 + 1 ] << " / " << vertices2[ i * 3 + 2 ];
}