Reading a float texture with glGetTexImage as int output?

0
votes

I'm trying to read a texture that's been loaded with floating-point values using my generic code for reading images, which tries to read it out as (8-bit) integer values.

I was expecting it to clamp the values to 0..1 and to basically make it look pretty horrible, but still recognizable. Instead, it's completely black, as if it read all black values.

The texture is GL_R32F format and I'm trying to read it as GL_UNSIGNED_BYTE with GL_RGBA as output.

Should this work? If not, what kind of thing should I be looking for?

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openglfloating-pointinttextures
What exactly is it that you are trying to accomplish? And why do you want OpenGL to do the conversion? Can't you just read it back as what it is and convert it yourself? - Nicol Bolas
I'm trying to read that texture using my default "read this texture and save as a PNG". Uploading (glTexImage) does conversions for you so I expected glGetTexImage to do the same. If this won't work I'll have to hack it up myself which is more code and more work... - dascandy
Mathematically, what conversion are you looking for? Given a floating-point value stored in the texture, what integer value do you want to get back? What is the math equation that you want applied to the values? - Nicol Bolas
Well... the same that loading an integer texture with floating point values would do. It converts 0...1 to 0...<integer max>. I was expecting 0...1 to be converted to 0...255 and to get a black&white image with over-saturated regions. Instead, it's black. - dascandy
Is glGetError() reporting error after glGetTexImage? - Mārtiņš Možeiko

1 Answers

1
votes

glGetTexImage should be able to return what you want (8 bits unsigned). Obviously, the image read back would not be as smooth as the original because of precision loss (32 bits to 8 per component).

However, I must say I don't think I've ever done this specifically with an R32F internal format... Try with different formats to see if you get different results. Also, make sure all the conditions for glGetTexImage to work are met (texture bound, no buffer bound to GL_PIXEL_PACK_BUFFER, etc.). See the doc for glGetTexImage for all conditions.