51 lines
2.1 KiB
GLSL
51 lines
2.1 KiB
GLSL
#include <flutter/runtime_effect.glsl>
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// The engine supplies the backing texture and its physical size.
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uniform vec2 u_texture_size;
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uniform vec2 u_origin;
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uniform vec2 u_extent;
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uniform float u_strength;
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uniform sampler2D u_background;
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out vec4 frag_color;
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vec2 sampleUV(vec2 point) {
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vec2 uv = point / u_texture_size;
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#ifdef IMPELLER_TARGET_OPENGLES
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uv.y = 1.0 - uv.y;
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#endif
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return clamp(uv, vec2(0.001), vec2(0.999));
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}
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void main() {
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vec2 point = FlutterFragCoord().xy;
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vec2 centre = u_origin + u_extent * 0.5;
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vec2 local = point - centre;
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float radius = max(u_extent.y * 0.5, 1.0);
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float spine = max(u_extent.x * 0.5 - radius, 0.0);
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vec2 outward = local - vec2(clamp(local.x, -spine, spine), 0.0);
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float distance = length(outward);
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vec2 normal = outward / max(distance, 0.001);
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float depth = radius - distance;
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float rim = 1.0 - smoothstep(0.0, radius * 0.52, depth);
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// Curved glass bends rays most at its edge, with subtle centre magnification.
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vec2 ray = centre + local / (1.0 + u_strength * 0.075)
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- normal * rim * rim * radius * u_strength * 0.23;
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vec4 colour = texture(u_background, sampleUV(ray));
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float dispersion = u_strength * rim * 0.80;
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colour.r = texture(u_background, sampleUV(ray + normal * dispersion)).r;
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colour.b = texture(u_background, sampleUV(ray - normal * dispersion)).b;
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// The curved rim catches nearby background light as well as transmitting it.
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// Reflection follows live pixels instead of being a painted white outline.
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float facing = max(0.0, dot(normal, normalize(vec2(-0.5, -0.8))));
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float edge_light = pow(rim, 4.0) * u_strength * facing;
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vec4 reflected = texture(u_background,
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sampleUV(point + normal * radius * 0.40));
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colour = mix(colour, reflected, min(edge_light * 0.22, 0.26));
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// A grazing-angle white reflection gives the curved rim visible thickness;
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// the broad centre continues to transmit the live, lightly softened scene.
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colour.rgb = mix(colour.rgb, vec3(colour.a), min(edge_light * 0.19, 0.22));
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float reflection = edge_light * 0.10;
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colour.rgb = min(colour.rgb + reflection * colour.a, vec3(colour.a));
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frag_color = colour;
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}
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