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#version 300 es
// Retro CRT Shader - FULLY OPTIMIZED
// Fixes: Resolution-aware scanlines, proper vignette, edge clamping,
// correct aberration direction, anti-aliased scanlines
precision highp float;
in vec2 v_texcoord;
uniform sampler2D tex;
out vec4 fragColor;
// --- CONFIGURATION ---
const float CURVATURE = 3.5;
const float SCANLINE_STRENGTH = 0.25;
// Approximate screen height in pixels (adjust to your resolution)
const float SCREEN_HEIGHT = 1080.0;
// Scanlines per screen height (lower = thicker lines)
const float SCANLINE_COUNT = 540.0;
const float ABERRATION = 0.002;
const float VIGNETTE_RADIUS = 1.00;
const float VIGNETTE_SOFTNESS = 0.45;
// Phosphor glow simulation
const float GLOW = 0.03;
vec2 curveUV(vec2 uv) {
uv = uv * 2.0 - 1.0;
vec2 offset = abs(uv.yx) / vec2(CURVATURE);
uv = uv + uv * offset * offset;
uv = uv * 0.5 + 0.5;
return uv;
}
void main() {
vec2 uv = curveUV(v_texcoord);
// Black bezel for out-of-bounds
if (uv.x < 0.0 || uv.x > 1.0 || uv.y < 0.0 || uv.y > 1.0) {
fragColor = vec4(0.0, 0.0, 0.0, 1.0);
return;
}
// FIXED: Clamp aberration samples to prevent edge artifacts
vec2 centerDist = uv - 0.5;
vec2 aberrOffset = centerDist * ABERRATION;
// FIXED: Correct direction - red focuses short, blue focuses long
float r = texture(tex, clamp(uv + aberrOffset, 0.0, 1.0)).r;
float g = texture(tex, uv).g;
float b = texture(tex, clamp(uv - aberrOffset, 0.0, 1.0)).b;
vec3 color = vec3(r, g, b);
// FIXED: Anti-aliased scanlines that don't shimmer during scroll
// Using smooth triangle wave instead of harsh sine
float scanlinePhase = uv.y * SCANLINE_COUNT * 2.0;
float scanline = abs(fract(scanlinePhase) - 0.5) * 2.0; // Triangle wave 0-1
scanline = smoothstep(0.0, 1.0, scanline); // Smooth it
float scanlineFactor = 1.0 - (SCANLINE_STRENGTH * (1.0 - scanline));
color *= scanlineFactor;
// Subtle phosphor glow (brightens slightly between scanlines)
color += GLOW * (1.0 - scanline);
// FIXED: Proper circular vignette with correct smoothstep bounds
float dist = length(centerDist) * 2.0; // 0 at center, ~1.414 at corners
float vignette = 1.0 - smoothstep(VIGNETTE_RADIUS, VIGNETTE_RADIUS + VIGNETTE_SOFTNESS, dist);
color *= vignette;
// Subtle brightness boost to compensate for darkening effects
color *= 1.1;
fragColor = vec4(clamp(color, 0.0, 1.0), 1.0);
}
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