Thanks Dave for the update, I believe Laurent just added support for that in trunk: ptr = Pointer.magic_cookie(12) glVertexPointer(3, GL_FLOAT, ptr) It looks like you are having fun with OpenGL and MacRuby, would you mind writing a small intro article for the MacRuby website? That would be really appreciated. Thanks, - Matt On Wed, Jan 12, 2011 at 1:29 PM, Dave Baldwin <dave.baldwin@dsl.pipex.com>wrote:
Just to give an answer for anyone finding this later.
On 21 Dec 2010, at 20:20, Dave Baldwin wrote:
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.
All the methods for loading the in vertex data work fine and the only problem (as alluded to) is how to pass an integer to a C function expecting a void * pointer.
There is no way to do this in MacRuby 0.8 and the only option is to write a small objective C stub to do this. One such stub looks like:
- (void) glVBOVertexPointer: (GLint) size type: (GLenum) type stride: (GLsizei) stride offset:(GLint) offset { glVertexPointer(size, type, stride, (void *) offset); }
and once you have built this and loaded it (see http://www.macruby.org/recipes/create-an-objective-c-bundle.html) then calling it
glVBOVertexPointer(3, type: GL_FLOAT, stride: strideInBytesBetweenVertices, offset: 0)
make everything work as expected.
Dave.
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