Step 3 GLSL

../../_images/step_03.png
step_03.glsl
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
// x, y position of the light
uniform vec2 lightPosition;
// Size of light in pixels
uniform float lightSize;

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Distance in pixels to the light
    float distanceToLight = length(lightPosition - fragCoord);

    // Normalize the fragment coordinate from (0.0, 0.0) to (1.0, 1.0)
    vec2 normalizedFragCoord = fragCoord/iResolution.xy;

    // Start our mixing variable at 1.0
    float lightAmount = 1.0;

    // Find out how much light we have based on the distance to our light
    lightAmount *= 1.0 - smoothstep(0.0, lightSize, distanceToLight);

    // We'll alternate our display between black and whatever is in channel 1
    vec4 blackColor = vec4(0.0, 0.0, 0.0, 1.0);

    // Our fragment color will be somewhere between black and channel 1
    // dependent on the value of b.
    fragColor = mix(blackColor, texture(iChannel1, normalizedFragCoord), lightAmount);
}