I have an openGL program that works if I use vertex arrays to store the
geometry data, but if I convert it to use an openGL vertex buffer object then
nothing is drawn. Has anyone got vertex buffer objects to work with MacRuby?
I am using 0.8 on 10.6.4
(In OpenGL a vertex buffer object just holds geometry but on the graphics card
so for large amounts of geometry will be significantly faster than a vertex
array where the geometry is held in the client's memory and copied to the
graphics card every time it is drawn).
The code is:
@vbo_buffer = Pointer.new('f', 1000)
... # initialise with vertex data (BYTES_IN_BUFFER
set up with the size of the vertex data)
# Get a buffer object id
cubeVBO = Pointer.new_with_type('I', 1)
glGenBuffers(1, cubeVBO)
@cubeVBO = cubeVBO[0]
glBindBuffer(GL_ARRAY_BUFFER, @cubeVBO)
# The vertex buffer object can be initialised in
several ways
case vbo_method
when :writeOnAllocate
# This call will allocate the vertex
buffer object and initialise it from @vbo_buffer
glBufferData(GL_ARRAY_BUFFER,
BYTES_IN_BUFFER, @vbo_buffer, GL_STATIC_DRAW)
when :writeAfterAllocate
nullPtr = Pointer.new("^I")
# This call will allocate the vertex
buffer object but not initialise it.
glBufferData(GL_ARRAY_BUFFER,
BYTES_IN_BUFFER, nullPtr, GL_STATIC_DRAW)
# Now initialise it.
glBufferSubData(GL_ARRAY_BUFFER, 0,
BYTES_IN_BUFFER, @vbo_buffer)
when :mapAfterAllocate
nullPtr = Pointer.new("^I")
# This call will allocate the vertex
buffer object but not initialise it.
glBufferData(GL_ARRAY_BUFFER,
BYTES_IN_BUFFER, nullPtr, GL_STATIC_DRAW)
# Get a pointer to the allocated buffer
and copy the data over manually.
buffer = glMapBuffer(GL_ARRAY_BUFFER,
GL_READ_WRITE).cast!('f')
(BYTES_IN_BUFFER / 4).times {|i|
buffer[i] = @vbo_buffer[i]} # copy as floats
glUnmapBuffer(GL_ARRAY_BUFFER)
end
Finally to draw the vertex buffer object
glBindBuffer(GL_ARRAY_BUFFER, @cubeVBO)
glEnableClientState(GL_VERTEX_ARRAY)
v = Pointer.new("^c") # gives us a null pointer -
need to pass in 0 in next call
glVertexPointer(3, GL_FLOAT, v)
glColor3f(1.0, 0.0, 0.0)
glDrawArrays(GL_QUADS, 0, 24) # 0 = start offset, 24 = number
of vertices
None of the three methods to load the vertex buffer object make a difference.
The other problem I will have is the colour data is interleaved in with the
vertex data so ideally I need to call:
glVertexPointer(3, GL_FLOAT, 12)
but this function needs to take a void* pointer so how do I create a pointer
with a value?
Dave.
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