CODEWITHSUNDEEP
c++openglglteximage2d
Daniel
Daniel

Reputation: 768

TexSubImage2D produces a garbled texture for specific images only

I'm trying to get a texture to be rendered on top of another one, like in the image below:

  Desired

However, only that image gets rendered properly. My other images get garbled and "twisted". If you look carefully, it's as if the rows were shifted:

  Actual

In the above example, I used the very same cat picture in the background. Both this cat picture, and all other images I generate end up garbled, except that one special picture, for some reason. I have looked at EXIF data, and other than the fact that it doesn't use sRGB, it is in the exact same format as the others. It has an alpha channel and everything.

I believe it has something to do with pixel alignment, given how the rows are shifted, but I have tried literally every possible combination of alignment and nothing as worked so far. Here is my code:

int height, width = 512;
m_pSubImage = SOIL_load_image("sample.png", &width, &height, 0, SOIL_LOAD_RGBA);

glGenTextures(1, &m_textureObj);
glBindTexture(m_textureTarget, m_textureObj);
...
glActiveTexture(TextureUnit);
glBindTexture(m_textureTarget, m_textureObj);
glTexSubImage2D(GL_TEXTURE_2D, 0, 20, 10, 100, 100, GL_RGBA, GL_UNSIGNED_BYTE, m_pSubImage);

The code for loading the background image is similar, except that it uses this call instead of glTexSubImage2D:

glTexImage2D(m_textureTarget, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_pImage);

Upvotes: 0

Views: 995

Answers (2)

Ben Voigt
Ben Voigt

Reputation: 283614

You don't appear to be checking for failures. The following failure modes of glTexSubImage2D are especially relevant here:

  • GL_INVALID_VALUE is generated if xoffset < 0, xoffset + width > w, yoffset < 0, yoffset + height > h, where w is the width and h is the height of the texture image being modified.

  • GL_INVALID_VALUE is generated if width or height is less than 0.

  • GL_INVALID_OPERATION is generated if the texture array has not been defined by a previous glTexImage2D or glCopyTexImage2D operation whose internalformat matches the format of glTexSubImage2D.

Upvotes: 0

Ben Voigt
Ben Voigt

Reputation: 283614

It appears that you aren't passing the width and height correctly to glTexSubImage2D. Note that you need the number of pixels stored per scanline, which is often not exactly the "logical" width of the image, but rounded up to a multiple of 4.

The difference between the "logical" and "storage" width will leave a few padding pixels left over on each scan line, which will be interpreted as the leftmost pixels of the next scanline, and accumulate as you move down the image. That creates the slant effect you observe.

Upvotes: 1

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