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Asked: 2026-06-17T13:29:36+00:00

I have a 6 vertex rectangle 100×100 in size, this i covered with a

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I have a 6 vertex rectangle 100×100 in size, this i covered with a 100×100 background image. now i would like to render two “sub textures” on top of it.

lets say i have two sub textures size 20×20 one of then i like to position at x:10 y:10 and the other x:50 and y:50

(these are actually to get used as masks on the background image.)

how should i go with this ? my first thought was to send a uniform vec2 with the position of the two sub textures info the fragment shader, but i cant really figure out how to convert those into texture2d(subtexture, coordinate) because texture2d takes 0-1 values. i cant really wrap my head around this, and i hope to get some pointers in what direction i should go.

(this is to be used on OpenGL ES 2.0)

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1 Answer

  1. Editorial Team

    Then I think what you’re really looking for is how to update a texture. In you case, the simplest method may be to use glTexSubImage2D. The following will do what you ask in your original post

    glTexSubImage2D( GL_TEXTURE_2D, 0, 10, 10, 20, 20, <format>, <type>, <subimage1> );
glTexSubImage2D( GL_TEXTURE_2D, 0, 50, 50, 20, 20, <format>, <type>, <subimage2> );

    where <format>, and <type> describe the pixels in the sub-texture stored at <subimage*>. There are quite a lot of additional answers in other questions; just search for glTexSubImage2D.

    A more complex method (for when things aren’t as simple as your problem) is to use framebuffer objects to render to textures (have search for that one too, if you need).

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