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Editorial Team
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Asked: 2026-05-24T09:54:56+00:00

I am using OpenGL 1.3 to do 2D sprite rendering and supporting both POTS

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I am using OpenGL 1.3 to do 2D sprite rendering and supporting both POTS (power of two size) textures and NPOTS (non power of two size) textures with TEXTURE_2D and TEXTURE_RECTANGLE_ARB respectively.

I had started with POTS textures (using TEXTURE_2D), which worked fine, but now I am adding NPOTS textures (using TEXTURE_RECTANGLE_ARB). This addition has caused the POTS textures (with TEXTURE_2D) to break.

By break I mean that the POTS textures are rendered as a grayscale gradient ranging from gray in the bottom left corner and white in the top right.

An extra point (discovered whilst trying to fix this error) – One big difference between TEXTURE_RECTANGLE_ARB and TEXTURE_2D is that the first uses non-normalised coordinates on the textures, whereas TEXTURE_2D uses normalised coordinates ([0.0,1.0]). I decided to check and replace the TEXTURE_2D’s normalised coordinates with non-normalised coordinates, and this removed the grayscale problem by creating another – it was rendering the wrong texture!

I.e. when using a POTS and an NPOTS texture, my POTS texture tries to render the NPOTS texture.

Does anyone have any idea why this might be happening? Thankyou!

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1 Answer

  1. Editorial Team

    Okay, so it turns out that it was a rather silly mistake, that was found in the original TEXTURE_2D code. I had forgotten to end the rendering with the correct glDisable!

    I.e. the rendering code began with glEnable(targetType), but did not end with glDisable(targetType) [where targetType was the correct choice of GL_TEXTURE_2D or GL_TEXTURE_RECTANGLE_ARB].

    I guess, somehow, the two rendering environments got intertwined.

    Lesson – make sure when you begin with glEnable that you end with glDisable.

    Edit: Considering the below comment, I did a little digging and found out about target presidence. The idea is presented in the beginning of this article:

    http://math.hws.edu/graphicsnotes/c4/s5.html

    “At most one texture target will be used when a surface is rendered. If several targets are enabled, 3D textures have precedence over 2D textures, and 2D textures have precedence over 1D. Except for one example later in this section, we will work only with 2D textures.”

    In terms of TEXTURE_RECTANGLE_ARBs precedence, this is described in the specification in section 10: http://www.opengl.org/registry/specs/ARB/texture_rectangle.txt

    I did not know about target priority or precedence at the time of the bug, so thanks to @datenwolf!

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