First, let me say that I have a working version of a game in opengl ES 1.1 on the iphone and
the android and I'm porting to OpenGL ES2 using the AMD SDK.
First, the simple problem... glGetIntegerv doesn't seem to provide correct query
values for GL_ARRAY_BUFFER_BINDING, GL_ELEMENT_ARRAY_BUFFER_BINDING,
and GL_ACTIVE_TEXTURE, For example, if I create an array buffer, upload appropriate vertex
data, execute the following
glBindBuffer (GL_ARRAY_BUFFER, verticesHandle);
GLint retrievedHandle; glGetIntegerv (GL_ARRAY_BUFFER_BINDING, &retrievedHandle);
and continue to draw it, everything works fine... If I log the above handles, then
verticesHandle will be some arbitrary value such as 6 that depends on when I created
it but retrievedHandle will always be 0. The same kind of thing happens for GL_ELEMENT_ARRAY_BUFFER_BINDING
and GL_ACTIVE_TEXTURE... Generally, I'm just not using glGetIntegerv since it's not required
but I was trying to use it for debugging.
The second problem is more fundamental... I've created a vertex buffer with less than 64k vertices
and a very large index buffer (more than 200k)...
I bind the vertex buffer handle, bind the index buffer handle, activate the appropriate vertex attributes
and execute
glDrawElements (GL_TRIANGLE_STRIP, size, GL_UNSIGNED_SHORT, offset);
and follow it by a test for an OpenGL error. Everything is perfect as long as the offset is small.
A typical scenario which goes wrong (i.e., generates an GL_INVALID_OPERATION error) occurs
when size = 594 and offset = 139658. The driver is apparently concluding that there must be
an error because the offset is larger than one GL_UNSIGNED_SHORT. But this is a mistake
because the indexes that must be in the range of the unsigned short are the indices used
to index into the vertices; i.e. THE ELEMENTS must be unsigned shorts (NOT THE START
OF THE SET OF INDICES).
To repeat, there is nothing wrong in having 100k of GL_UNSIGNED_SHORT indices provided
they index into a vertex array with fewer than 65k vertices.
