CODEWITHSUNDEEP
glsl
رامي عبد الله
رامي عبد الله

Reputation: 329

Comparison between two integers in GLSL

I want to build a fragment shader, and I realized that the comparison between two int in glsl 1.5.0 will return always false. I am using integers as an enumeration in a method parameter. This is the problem in a simple way and this code has the same result.

void main(){
    int x = 5;
    #if(x == 5)
        gl_FragColor = vec4(1.0);
    #else
        gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
    #endif
}

I tried this code and the condition x == int(2) will return always true!

void main(){
    int x = 5;
    #if(x == int(2))
        gl_FragColor = vec4(1.0);
    #else
        gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
    #endif
}

So, what should I do to compare two integers in the right way?

Upvotes: 2

Views: 1856

Answers (1)

Rabbid76
Rabbid76

Reputation: 210948

#if, #else and #endif are preprocessor statements. But int x = 5; is a local variable. The preprocessor processes the source string, it is part of the comoilation process, but it is done before the actual compilation. The variable x has no meaning for the preprocessor.

A x for the preprocessor can be defines a follow:

#define x 5

#if(x == 5)
        gl_FragColor = vec4(1.0);
#else
        gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
#endif

But a glsl if statement start with the keyword if followed by a bool-expression and a statement. Optional followed by the keyword else and another statement:

int x = 5;
if (x == 5)
{
    gl_FragColor = vec4(1.0);
}
else
{
    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}

In this case the curly braces can be skipped, because in each case there is only a single statement.

Note, a ternary operator can be used, too:

gl_FragColor = x==5 ? vec4(1.0) : vec4(1.0, 0.0, 0.0, 1.0);

This all can be read in the OpenGL Shading Language 1.50 Specification in detail. The preprocessor is explained in chapter "3.3 Preprocessor", the if statement is specified in chapter "6.2 Selection" and and the Ternary operator in chapter "5.8 Assignments"

Upvotes: 2

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