Hi,
On Tue, 2005-10-11 at 13:45 +0200, Oliver Kutter wrote:
> Hi Gerrit,
>
> that would have been to beautifully, if that would had worked completely
> at once.
>
> Yes, it works, but not really. At the beginning, I put my particle
> positions (as float texture) initially to the shader and want to compute
> their new positions. For this texture I have the following properties.
> Target: GL_TEXTURE_2D, InternalFormat: GL_RGBA32F_ARB. In the shader, I
> access the sampler2D texture by the texture2D command.
>
> I use your glReadBuffer to get some kind of output for the current
> positions stored in that texture, initially they are like this:
>
> 45.078125 3.000000 50.000000 0.000000
> 45.234375 3.000000 50.000000 0.000000
> 45.390625 3.000000 50.000000 0.000000
> 45.546875 3.000000 50.000000 0.000000
> 45.703125 3.000000 50.000000 0.000000
> 45.859375 3.000000 50.000000 0.000000
> 46.015625 3.000000 50.000000 0.000000
> 46.171875 3.000000 50.000000 0.000000
> 46.328125 3.000000 50.000000 0.000000
> 46.484375 3.000000 50.000000 0.000000
>
> This output is correct!
>
> Then I write the positions back to the texture. In the next Rendering
> pass, I want to load the output texture (GL_TEXTURE_RECTANGLE_NV,
> GL_FLOAT_RGBA32_NV) as input texture and that does not work, because the
> properties are not correct.
> Thus, I changed the properties of my first input texture to the
> properties of the output texture. In the shader, I changed sampler2D to
> sampler2DRect and the texture2D command to texture2DRect.
>
> But now my particle positions are initially all the same (all like the
> first position of the correct output above), like this:
>
> 45.078125 3.000000 50.000000 0.000000
> 45.078125 3.000000 50.000000 0.000000
> 45.078125 3.000000 50.000000 0.000000
> 45.078125 3.000000 50.000000 0.000000
> 45.078125 3.000000 50.000000 0.000000
> 45.078125 3.000000 50.000000 0.000000
> 45.078125 3.000000 50.000000 0.000000
> 45.078125 3.000000 50.000000 0.000000
> 45.078125 3.000000 50.000000 0.000000
> 45.078125 3.000000 50.000000 0.000000
>
> Do you have an idea, why? Do I have to do something with the texture
> coordinates?
most likely, normal texture coordinates (minus wrapping) are between 0
and 1, for GL_TEXTURE_RECTANGLE_NV this changes to 0 - texture width and
0 - texture height. So if you switched to texture2DRect and were still
using old 0 - 1 texture coordinates you should get the result you see.
The easiest test would be to modify the fragment program from
texture2DRect(sampler, vec2(x, y)); // x,y {0 - 1}
to
texture2DRect(sampler, vec2(x * textureWidth, y * textureHeight));
if this gives you the expected results the problems are indeed the
different texture coordinates.
regards,
gerrit
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