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oliver_mpt

OpenGL Newbie color question

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Hello ! I'm new to DirectX, coming from OpenGL. I've noticed that 3D objects must have a color parameter for each vertex. In the case of an object with uniform color, I would like to change its color, in order to redraw it several times with different colors. Is there a way without changing the color in all vertices ? it seems pretty inneficient to me. In particular, we have the option to store the vertex and index buffers in different memories to optimize loading speed. In that case accessing to all vertices to change color is particularly not efficient. Is there something like glColor in OpenGL that allow me to change the current color - DO I need absolutely to store it in ALL vertex ? regards, Olivier

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Are you referring to the fixed function pipeline?

IMHO the best solution is to write a simple shader.
Don't use the vertex color, set a float4 parameter and in the pixel shader just output that color.

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You don't *have* to have colour per vertex, unless you are using the fixed function pipeline to render with. You could have a vertex structure like this...

float x, y, z; // Position
float nx, ny, nz; // Normal

And then use a shader to render with what ever colour you like.

If you *are* using the FFP then I think the only way is with vertex format...

float x, y, z; // Position
float nx, ny, nz; // Normal
DWORD colour; // Colour

Which means changing each vertex colour before rendering - which shouldn't be a major problem depending on how many vertices you are dealing with.

For the most efficient way, I think go the shader route - FFP rendering is becoming obsolete.

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Hello

Thanks for all the answers,

I'm not sure I unsderstand, though.
doest it read FFP = directX9 and shader route = DX10 ?

I need absolutely Windows XP compatibility, so as far as I understand no DX10.

can you clarify a bit for me ? (I told you: newbie question ;-))

Oliver

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For D3D9, I'd suggest using pixel shaders whether you use FFP or shaders for the vertices. They're simply a lot easier to understand and program than texture stages.

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