// x, y position of the light
uniform vec2 lightPosition;
// Size of light in pixels
uniform float lightSize;
float terrain(vec2 samplePoint)
{
float samplePointAlpha = texture(iChannel0, samplePoint).a;
float sampleStepped = step(0.1, samplePointAlpha);
float returnValue = 1.0 - sampleStepped;
return returnValue;
}
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;
float shadowAmount = terrain(normalizedFragCoord);
lightAmount *= shadowAmount;
// 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);
}