The following code doesn't actually seem to copy data correctly on either an HD7750 or an HD6450
GLuint tempVBO;
glGenBuffers(1, &tempVBO);
glBindBuffer(GL_COPY_READ_BUFFER, tempVBO);
glBindBuffer(GL_ARRAY_BUFFER, srcVBO);
glBufferData(GL_COPY_READ_BUFFER, oldByteCount, NULL, GL_STATIC_COPY);
glCopyBufferSubData(GL_ARRAY_BUFFER, GL_COPY_READ_BUFFER, 0, 0, oldByteCount);
glBufferData(GL_ARRAY_BUFFER, newByteCount, NULL, GL_STATIC_DRAW);
glCopyBufferSubData(GL_COPY_READ_BUFFER, GL_ARRAY_BUFFER, 0, 0, oldByteCount);
glBindBuffer(GL_COPY_READ_BUFFER, 0);
glBindBuffer(GL_ARRAY_BUFFER,0);
glDeleteBuffers(1, &tempVBO);
After running that code , if the data is read back using map buffer it will be all zeros or garbage. However if any other memory operation is performed it'll work.
For instance the following code will correctly copy the data between buffers. The original code works fine on the various NVIDIA cards I've tested.
GLuint tempVBO;
glGenBuffers(1, &tempVBO);
glBindBuffer(GL_COPY_READ_BUFFER, tempVBO);
glBindBuffer(GL_ARRAY_BUFFER, srcVBO);
glBufferData(GL_COPY_READ_BUFFER, oldByteCount, NULL, GL_STATIC_COPY);
//glSubBufferData, glBufferData with one byte, whatever
glMapBuffer(GL_COPY_READ_BUFFER, GL_READ_ONLY);
glUnmapBuffer(GL_COPY_READ_BUFFER);
glCopyBufferSubData(GL_ARRAY_BUFFER, GL_COPY_READ_BUFFER, 0, 0, oldByteCount);
glBufferData(GL_ARRAY_BUFFER, newByteCount, NULL, GL_STATIC_DRAW);
glMapBuffer(GL_ARRAY_BUFFER, GL_READ_ONLY);
glUnmapBuffer(GL_ARRAY_BUFFER);
glCopyBufferSubData(GL_COPY_READ_BUFFER, GL_ARRAY_BUFFER, 0, 0, oldByteCount);
glBindBuffer(GL_COPY_READ_BUFFER, 0);
glBindBuffer(GL_ARRAY_BUFFER,0);
glDeleteBuffers(1, &tempVBO);
What am I missing here?
