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I'm trying to send a boolean to an OpenGL glsl shader.

Currently I have this in the shader:

uniform bool foo;

And I use this to set it:

glUniform1i(glGetUniformLocation(shader, "foo"), true);

There doesn't seem to be a glUniform1b, so I'm setting it as an integer. This seems to work fine.

Is there any problem with this approach? Is it portable, or could it break on other graphics cards / drivers? I'm using OpenGL 4.3 at the moment.

Jongware
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Jan Rüegg
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  • As far as I know it has something to do with 4-byte alingment (boolean is 1 byte so either way 3 additional padding bytes will be added at the end) so using boolean is not efficient and maby even deprecated in OpenGL – Amadeusz Nov 13 '15 at 10:09
  • @Amadeusz it's certainly not deprecated. – Bartek Banachewicz Nov 13 '15 at 10:39

2 Answers2

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§ 4.1 Basic Types The OpenGL Shading Language supports the following basic data types, grouped as follows:

  • bool a conditional type, taking on values of true or false
  • bvec2 a two-component Boolean vector
  • bvec3 a three-component Boolean vector
  • bvec4 a four-component Boolean vector

...

§ 4.1.2 Booleans To make conditional execution of code easier to express, the type bool is supported. There is no expectation that hardware directly supports variables of this type. (...)

As for setting:

§ 2.2.1 (...) When state values are specified using a different parameter type than the actual type of that state, data conversions are performed as follows:

  • When the type of internal state is boolean, zero integer or floating-point values are converted to FALSE and non-zero values are converted to TRUE.
Bartek Banachewicz
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0

The size of a glsl bool is 32-bits which is identical to an int, so yes, you can set it like that.

And no, it won't break on other graphics cards / drivers for OpenGL.

The golden apple
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    *"integer below or equal to zero is considered false"* The other answer claims that non-zero integers are always false. *"bool occupies 1-byte"* I'm not sure about it, the other answer claims that *"no expectation that hardware directly supports variables of this type"*. – HolyBlackCat Jul 21 '21 at 07:22