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Rather than have two separate shaders in my OpenGL code (one for when a texture is bound, one for when none is bound) I usually go for one shader program which handles both. This is my usual fragment shader:

#version 330

uniform bool textured;
uniform sampler2D sampler;

in vec4 fColor;
in vec2 tCoord;

out vec4 final_color;

void main()
{
    vec4 texel = vec4(1.0, 1.0, 1.0, 1.0);
    if (textured)
        texel = texture(sampler, tCoord);
    final_color = fColor * texel;
}

In a modern OpenGL profile, this compiled but did not output anything but black pixels (alternatively in LWJGL legacy profile, it outputted regular colors if textured == false and textured if textured == true). I don't see any reason that this wouldn't work, but what is a method which would work for both textured and untextured fragments?

EDIT:

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1 Answer 1

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If you don't bind a texture to the slot, the result of sampling is basically undefined (though it's often vec4(0)).

To fix your issue, create a white 1x1 texture and assign it to sampler when you're using this shader without a texture.

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  • \$\begingroup\$ Even though I only reference it if textured == true? \$\endgroup\$ Commented Dec 26, 2015 at 22:39
  • \$\begingroup\$ @ZachGoethel Ah, missed that, sorry. In that case, there could easily be a bug in the textured uniform setting code. But there could also be undefined behavior (shader compiles to mix(texel, texture(..), textured), texture returns NaN). Either way, the approach I described works without the branch and extra parameter. \$\endgroup\$
    – snake5
    Commented Dec 26, 2015 at 22:47
  • \$\begingroup\$ But do you have recommended changes? To set textured I use glUniform1i([location getter], 0 or 1). \$\endgroup\$ Commented Dec 26, 2015 at 22:51
  • \$\begingroup\$ @ZachGoethel There's nothing to change there. But have you actually checked that the code runs, and at the right time (after glUseProgram, before the draw call)? P.S. stackoverflow.com/a/21030831/1648140 \$\endgroup\$
    – snake5
    Commented Dec 26, 2015 at 22:56
  • \$\begingroup\$ I'm adding links to my main.cpp and shader.hpp, but I won't be able to add more until tomorrow afternoon. \$\endgroup\$ Commented Dec 26, 2015 at 23:00

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