CODEWITHSUNDEEP
opengl-esglslshaderwebglfragment-shader
solomancode
solomancode

Reputation: 55

Color a set of fragments in fragment shader

My goal is to color a set of fragments determined by the interpolation between two points. Below the code I've written, It didn't work.!.

I also added some comments, Probably there are some mistakes I made or something that I misunderstood.

Thank you for your help.

#ifdef GL_ES
precision highp float;
#endif

uniform vec2 u_resolution;

void main(){
    vec2 position = gl_FragCoord.xy / u_resolution;
    vec4 color = vec4(0.97, 0.1, 0.53, 1.0);
    
    // center (hopefully)
    vec2 P1 = vec2(0.0,0.0);
    // top right
    vec2 P2 = vec2(1.0,1.0);
    
    // generate 100 points between P1...P2
    for(float i = 0.0; i < 1.0; i+=0.01) {
        float lerpX = mix(P1.x, P2.x, i);
        float lerpY = mix(P1.y, P2.y, i);
        vec2 interpolatedPoint = vec2(lerpX, lerpY);

        // check if current fragment is one of the
        // interpolated points and color it
        if (position.x == interpolatedPoint.x) {
            gl_FragColor = color;
        } else {
            discard;
        }
    }
}

Upvotes: 1

Views: 710

Answers (2)

Rabbid76
Rabbid76

Reputation: 210878

position.x == interpolatedPoint.x is a floating point comparison and is almost never evaluated as true. Your code discards all fragments. Implement a floating point comparison. Calculate the absolute value of the difference between the two values and compare it with an epsilon:

if (distance(position, interpolatedPoint) <= 0.01) {
    gl_FragColor = color;
}

Upvotes: 1

solomancode
solomancode

Reputation: 55

WORKING SOLUTION

#ifdef GL_ES
precision highp float;
#endif

uniform vec2 u_resolution;

void main(){
    vec2 position = gl_FragCoord.xy / u_resolution;
    vec4 color = vec4(0.97, 0.1, 0.53, 1.0);
    
    // center (hopefully)
    vec2 P1 = vec2(0.0,0.0);
    // top right
    vec2 P2 = vec2(1.0,1.0);
    
    // generate 100 points between P1...P2
    for(float i = 0.0; i < 1.0; i+=0.01) {
        float lerpX = mix(P1.x, P2.x, i);
        float lerpY = mix(P1.y, P2.y, i);
        vec2 interpolatedPoint = vec2(lerpX, lerpY);

        // check if current fragment is one of the
        // interpolated points and color it
        if (distance(position, interpolatedPoint) <= 0.01) {
            gl_FragColor = color;
        }
    }
}

Upvotes: 1

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