50 lines
2.0 KiB
GLSL
50 lines
2.0 KiB
GLSL
#version 330 core
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// Feature 9: PPI Shoreline / Terrain
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// Each vertex encodes (bearingDeg, rangeMiles) in polar radar coordinates.
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// The vertex shader converts to NDC and computes sweep-based fade on the GPU,
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// so the geometry buffer is static — only uniforms change each frame.
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layout(location = 0) in vec2 aBearingRange; // x = bearing °CW-from-N, y = range miles
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uniform vec2 uCenter; // NDC centre of PPI scope
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uniform float uPpiRx; // ppiR * 2.0 / W (one full-radius in NDC, x axis)
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uniform float uPpiRy; // ppiR * 2.0 / H (one full-radius in NDC, y axis)
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uniform float uMaxRange; // current max range (miles)
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uniform float uSweepAngle; // current sweep angle (degrees CW from N)
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uniform float uSweepDegPS; // sweep speed (degrees / second)
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uniform float uPersist; // phosphor persistence duration (seconds)
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out float vFade; // 0..1 brightness multiplier
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out float vActive; // 1.0 when sweep head is over this point
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const float PI = 3.14159265358979;
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const float THRESH = 3.5; // degrees — active window around sweep head
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void main()
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{
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float bearDeg = aBearingRange.x;
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float rangeMi = aBearingRange.y;
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float rangeFrac = rangeMi / uMaxRange;
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// Push out-of-range points outside the NDC clip volume
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if (rangeFrac > 1.0) {
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gl_Position = vec4(2.0, 2.0, 2.0, 1.0);
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vFade = 0.0;
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vActive = 0.0;
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return;
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}
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// Convert polar radar coords → NDC
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// North (0°) = +Y in NDC; East (90°) = +X in NDC
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float bearRad = bearDeg * PI / 180.0;
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float nx = uCenter.x + rangeFrac * uPpiRx * sin(bearRad);
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float ny = uCenter.y + rangeFrac * uPpiRy * cos(bearRad);
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gl_Position = vec4(nx, ny, 0.0, 1.0);
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gl_PointSize = 2.0;
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// Degrees the sweep has travelled past this point since last illumination
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float angBehind = mod(uSweepAngle - bearDeg + 360.0, 360.0);
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float timeSinceLit = angBehind / uSweepDegPS;
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vFade = clamp(1.0 - timeSinceLit / uPersist, 0.0, 1.0);
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vActive = (angBehind < THRESH) ? 1.0 : 0.0;
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}
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