117 lines
4.0 KiB
GLSL
117 lines
4.0 KiB
GLSL
/*
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* MIT License
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* Author: Mark Allyn
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*
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* sweep.frag — phosphor accumulation update shader.
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*
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* For each texel in the 1024×1024 phosphor FBO:
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* 1. Decay the previous frame's energy by u_decayFactor.
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* 2. If the texel's PPI bearing falls within the current sweep arc
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* [u_beamAnglePrev, u_beamAngle], add contributions from:
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* - range rings (beam-painted per the P7 spec)
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* - target echoes
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* 3. Output the updated single-channel energy value.
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*
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* PPI convention: north = +y, east = +x; bearing = atan2(x, y)
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* in degrees, clockwise from north.
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*/
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#version 330 core
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in vec2 vTexCoord;
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layout(location = 0) out vec4 fragOut; // .r = energy; .gba unused
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uniform sampler2D u_prevPhosphor; // previous frame's energy texture (GL_R32F)
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uniform float u_decayFactor; // exp(-decay_rate * dt)
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uniform float u_beamAngle; // current beam angle, degrees CW from north
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uniform float u_beamAnglePrev; // beam angle at previous frame
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uniform float u_sweepBg; // ambient sweep-line energy (makes beam visible)
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uniform float u_halfBeamDeg; // half-beamwidth for target blobs (display widening)
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// Targets: .x = range_norm (0-1), .y = bearing_deg, .z = brightness, .w = size_norm
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uniform vec4 u_targets[32];
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uniform int u_targetCount;
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// Range rings: up to 4 normalised radii
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uniform float u_ringRadii[4];
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uniform int u_ringCount;
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uniform float u_ringWidth; // half-width in normalised range units
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uniform float u_ringBrightness;
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// ----------------------------------------------------------------
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// Smallest unsigned angular distance between two bearings [0,360)
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float angleDiff(float a, float b) {
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float d = mod(abs(a - b), 360.0);
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return (d > 180.0) ? (360.0 - d) : d;
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}
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// True if bearing b is inside the arc [prev, curr] swept this frame.
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// Handles the 0/360 wraparound when the sweep crosses north.
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bool inSweep(float b, float prev, float curr) {
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if (curr >= prev) {
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return (b >= prev && b <= curr);
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}
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// Wraparound: arc crosses 360→0
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return (b >= prev || b <= curr);
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}
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// ----------------------------------------------------------------
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void main() {
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vec2 pos = vTexCoord * 2.0 - 1.0; // PPI coords: (-1,-1) SW … (+1,+1) NE
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float rng = length(pos);
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if (rng > 1.0) {
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fragOut = vec4(0.0);
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return;
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}
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// Bearing: clockwise from north — atan2(east, north) = atan2(x, y)
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float brg = degrees(atan(pos.x, pos.y));
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if (brg < 0.0) brg += 360.0;
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// Decay previous value
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float energy = texture(u_prevPhosphor, vTexCoord).r * u_decayFactor;
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if (inSweep(brg, u_beamAnglePrev, u_beamAngle)) {
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float contrib = u_sweepBg; // beam passage gives a faint ambient glow
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// ---- Range rings (painted at every bearing as beam sweeps) ----
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for (int i = 0; i < u_ringCount; i++) {
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float d = abs(rng - u_ringRadii[i]);
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if (d < u_ringWidth) {
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float w = 1.0 - d / u_ringWidth;
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contrib = max(contrib, u_ringBrightness * w * w);
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}
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}
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// ---- Target echoes ----
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for (int i = 0; i < u_targetCount; i++) {
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float tRng = u_targets[i].x;
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float tBrg = u_targets[i].y;
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float tBrt = u_targets[i].z;
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float tSize = u_targets[i].w;
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if (tRng <= 0.0 || tBrt <= 0.0) continue;
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// Angular proximity: beam must be sweeping over the target's bearing
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float dBrg = angleDiff(brg, tBrg);
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if (dBrg >= u_halfBeamDeg) continue;
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// Range proximity: pixel must be within the target blob
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float dRng = abs(rng - tRng);
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if (dRng >= tSize) continue;
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float bw = 1.0 - dBrg / u_halfBeamDeg; // angular taper
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float rw = 1.0 - dRng / tSize; // range taper
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contrib = max(contrib, tBrt * bw * rw);
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}
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energy = max(energy, contrib);
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}
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fragOut = vec4(clamp(energy, 0.0, 1.0), 0.0, 0.0, 1.0);
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}
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