first build attempt

shaders/phosphor.frag

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+/*
+ * MIT License
+ * Author: Mark Allyn
+ *
+ * phosphor.frag — maps the single-channel phosphor energy texture to
+ * the P7 colour sequence (blue → green → yellow-green → dark) and
+ * applies a simple inline bloom (box-filter glow) to bright pixels.
+ *
+ * Coordinate system: gl_FragCoord.xy in GL viewport pixels (origin
+ * bottom-left). Scope centre is passed as u_scopeCenter in the same
+ * coordinate system.
+ */
+#version 330 core
+
+out vec4 fragColor;
+
+uniform sampler2D u_phosphor;   // GL_R32F phosphor energy FBO
+uniform vec2  u_scopeCenter;    // scope centre in GL viewport pixels (bottom-left origin)
+uniform float u_scopeRadius;    // scope radius in pixels
+uniform float u_gain;           // receiver gain [0,1] — scales brightness
+uniform float u_bloomStep;      // UV step for bloom sample (≈ 2.5 / FBO_SIZE)
+uniform float u_bloomStrength;  // additive blend weight for bloom
+
+// P7 energy thresholds (match settings.h)
+const float T_BLUE  = 0.82;
+const float T_GREEN = 0.55;
+const float T_YGREE = 0.22;
+const float T_DARK  = 0.03;
+
+// P7 colour anchors
+const vec3 C_BLUE  = vec3(0.30, 0.70, 1.00);
+const vec3 C_GREEN = vec3(0.05, 1.00, 0.30);
+const vec3 C_YGREE = vec3(0.50, 1.00, 0.05);
+const vec3 C_YELLW = vec3(0.70, 0.70, 0.00);
+const vec3 C_BLACK = vec3(0.00, 0.00, 0.00);
+
+vec3 p7Color(float e) {
+    if (e >= T_BLUE)
+        return mix(C_GREEN, C_BLUE,  (e - T_GREEN) / (T_BLUE  - T_GREEN));
+    if (e >= T_GREEN)
+        return mix(C_YGREE, C_GREEN, (e - T_YGREE) / (T_GREEN - T_YGREE));
+    if (e >= T_YGREE)
+        return mix(C_YELLW, C_YGREE, (e - T_DARK ) / (T_YGREE - T_DARK ));
+    if (e >= T_DARK)
+        return mix(C_BLACK, C_YELLW, e / T_DARK);
+    return C_BLACK;
+}
+
+void main() {
+    // Fragment position relative to scope centre
+    vec2 delta = (gl_FragCoord.xy - u_scopeCenter) / u_scopeRadius;
+    float dist = length(delta);
+
+    if (dist > 1.0) {
+        fragColor = vec4(0.0);   // outside scope circle — transparent black
+        return;
+    }
+
+    // Map from PPI delta [-1,+1] to phosphor texture UV [0,1]
+    // delta.x = east, delta.y = north (both y directions already match)
+    vec2 uv = delta * 0.5 + 0.5;
+
+    float energy = texture(u_phosphor, uv).r * u_gain;
+
+    // Inline bloom: weighted box-filter over a 5×5 neighbourhood
+    float bloom = 0.0;
+    float wsum  = 0.0;
+    for (int dx = -2; dx <= 2; dx++) {
+        for (int dy = -2; dy <= 2; dy++) {
+            float w = exp(-float(dx*dx + dy*dy) * 0.45);
+            float e = texture(u_phosphor, uv + vec2(dx, dy) * u_bloomStep).r;
+            bloom += e * w;
+            wsum  += w;
+        }
+    }
+    bloom = (bloom / wsum) * u_bloomStrength;
+
+    float finalE = clamp(energy + bloom, 0.0, 1.0);
+    vec3  col    = p7Color(finalE);
+
+    // Soft-edge vignette at the scope boundary
+    float edge  = smoothstep(1.0, 0.97, dist);
+    fragColor   = vec4(col * edge, 1.0);
+}