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mcphist

OpenGL Texture deformation

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mcphist    122
Hi people. Look this two images: The first is my original sphere; the second is how I see with OpenGl. It has a deformation on the left side. I've tried everything: GL_LINEAR, GL_NEAREST, GL_CLAMP, etc. I'm using alpha testing for not drawing pink pixels. I've tried with BLEND, but it doesn't work too. Almost every texture that I have, has a minor deformation when I see with OpenGl. But this seems to happen when the texture is very small. For example, my sphere is 45x43. If I scale the QUAD, the texture automatically scale too, and it looks perfect. Is there a way for see a texture exactly like I made in Paint, for example? Thanks in advance!

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swordfish    276
What deformation?
The top image has a circle with the left and top edges slightly trimmed off.
The bottom image has a circle with the bottom and right edges trimmed off.
Conclusion: your texture is flipped across both axes. Invert your UV coordinates and see if that doesn't fix it.

The 'deformation' you are seeing is probably due to the quality of the image you are using for the texture. Can we see the actual image file so that we can be sure?

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mcphist    122
Ok, I'll scale the image:





The first is my original image, a 24 bits bitmap. In the second image, the deformation is marked with a blue rectangle. This DOESN'T happen if I scale the QUAD.

Also, note this:




The first is my original image, again a 24 bits bitmap. In the second image, I rotated with glrotatef 90 degrees. Note the little deformation.

All this DOESN'T happen if I scale the QUAD, very strange.

What can I do?

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KulSeran    3267
You should consider using an orthographic projection so that screen pixels can directly match up to your texture pixels.
Then you need to draw your textured quad to exactly the same screen size in pixels as your texture you loaded onto it.

Also note that you may need to fix up your UV coords on the texture so that
on a 64x64 image you have UV's of
0 + 1/128
1 - 1/128
(something i read some where about .5 pixel offsets being better than directly on the corners of a pixel)

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mcphist    122
Thanks for the answer. I'm using an orthographic projection, and my QUAD is the same size in pixels like my texture. For example, my green sphere is 45x43.


width = 45
height = 43

p_V = 45/64
p_U = 43/64

glBegin(GL_QUADS);

glTexCoord2f( 0, p_V ); glVertex2f( 0, 0 );

glTexCoord2f( p_U, p_V ); glVertex2f( width, 0 );

glTexCoord2f( p_U, 0 ); glVertex2f( width, height );

glTexCoord2f( 0, 0 ); glVertex2f( 0, height );

glEnd();



Anyway, I'm sure that the texture's coords and all that is ok, because if I scale the QUAD ( glVertex2f( width = 145, 0) glVertex2f( height = 143, 0) ) the texture is displayed perfectly, without imperfections.

I'm sure that I'm forgetting some texture's parameter, like GL_LINEAR, GL_NEAREST, etc.. but I can't find it.

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