Textures from SDL upside down
Hi, I am using HOpenGL in combination with hsSDL (http://darcs.haskell.org/~lemmih/hsSDL). This works great except for texture loading. All my textures are mirrored over the v-axis. So the top of a texture becomes the bottom. I first thought that I got the texture coordinates wrong. But the textures are also flipped on the GLU quadrics. Is there some way to tell (H)OpenGL that a texture is mirrored? I tried glPixelStore parameters but I don't think it is possible that way. Perhaps it is possible to change a hsSDL surface before loading the pixel data. Any advice is welcome. regards, Bas van Dijk
On Tuesday 06 March 2007 00:25, Bas van Dijk wrote:
I am using HOpenGL in combination with hsSDL (http://darcs.haskell.org/~lemmih/hsSDL). This works great except for texture loading. All my textures are mirrored over the v-axis. So the top of a texture becomes the bottom. I first thought that I got the texture coordinates wrong. But the textures are also flipped on the GLU quadrics.
IIRC, in SDL the y-coordinate increases when going down the screen, while OpenGL uses the usual mathematical convention of y increasing when going up. Therefore your images are flipped, I guess.
Is there some way to tell (H)OpenGL that a texture is mirrored? I tried glPixelStore parameters but I don't think it is possible that way. Perhaps it is possible to change a hsSDL surface before loading the pixel data. Any advice is welcome.
Usually the easiest and most efficient way is to simply flip your t texture coordinate, i.e. use 1-t instead of t. Using pixelStore should be possible, too (using negative offsets etc.), but often this is not really needed. Cheers, S.
On 3/13/07, Sven Panne
On Tuesday 06 March 2007 00:25, Bas van Dijk wrote:
I am using HOpenGL in combination with hsSDL (http://darcs.haskell.org/~lemmih/hsSDL). This works great except for texture loading. All my textures are mirrored over the v-axis. So the top of a texture becomes the bottom. I first thought that I got the texture coordinates wrong. But the textures are also flipped on the GLU quadrics.
IIRC, in SDL the y-coordinate increases when going down the screen, while OpenGL uses the usual mathematical convention of y increasing when going up. Therefore your images are flipped, I guess.
Is there some way to tell (H)OpenGL that a texture is mirrored? I tried glPixelStore parameters but I don't think it is possible that way. Perhaps it is possible to change a hsSDL surface before loading the pixel data. Any advice is welcome.
Usually the easiest and most efficient way is to simply flip your t texture coordinate, i.e. use 1-t instead of t.
Texture coordinates are not always guarnteed to be in the [0,1] range though. So a coordinate of 1.2 would become -0.2 which will not always sample the correct texel (depending on texture wrapping mode). -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862
participants (3)
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Bas van Dijk -
Sebastian Sylvan -
Sven Panne