civ14/Resources/Textures/Shaders/gradient_circle_mask.swsl

// Has 2 circles, an inner one that is unaffected and an outer one. Anything past the outer one is full red
// and in-between is a gradient.

light_mode unshaded;

uniform highp vec3 color;
uniform highp float time;
// Uniforms because it makes testing way easier. If needed make it const.
uniform highp float outerCircleRadius;
uniform highp float outerCircleMaxRadius;
uniform highp float innerCircleRadius;
uniform highp float innerCircleMaxRadius;
uniform highp float darknessAlphaOuter;

const highp float darknessAlphaInner = 0.0;

void fragment() {
	highp vec2 pixelSize = vec2(1.0/SCREEN_PIXEL_SIZE.x, 1.0/SCREEN_PIXEL_SIZE.y);
	highp vec2 pixelCenter = pixelSize*0.5;
	highp float distance = length(FRAGCOORD.xy - pixelCenter);
    
	highp float innerRadius = innerCircleRadius + time * (innerCircleMaxRadius - innerCircleRadius);
	highp float outerRadius = outerCircleRadius + time * (outerCircleMaxRadius - outerCircleRadius);
    
	if(distance > outerRadius) {
		COLOR = vec4(color.x, color.y, color.z, darknessAlphaOuter);
	}
	else if(distance < innerRadius) {
		COLOR = vec4(0.0, 0.0, 0.0, darknessAlphaInner);
	}
	else {
        	highp float ratio = (distance - innerRadius) / (outerRadius - innerRadius);
		highp float alpha = darknessAlphaInner + (darknessAlphaOuter - darknessAlphaInner) * ratio;
		COLOR = vec4(color.x, color.y, color.z, alpha);
	}
}