From cc988bdeb59826df4a07562e1ea97e2128464d62 Mon Sep 17 00:00:00 2001
From: hizzlekizzle <hizzlekizzle@users.noreply.github.com>
Date: Tue, 27 Sep 2022 10:17:59 -0500
Subject: [PATCH] Create analog_overshoot.slang

---
 ntsc/shaders/analog_overshoot.slang | 105 ++++++++++++++++++++++++++++
 1 file changed, 105 insertions(+)
 create mode 100644 ntsc/shaders/analog_overshoot.slang

diff --git a/ntsc/shaders/analog_overshoot.slang b/ntsc/shaders/analog_overshoot.slang
new file mode 100644
index 0000000..f96f055
--- /dev/null
+++ b/ntsc/shaders/analog_overshoot.slang
@@ -0,0 +1,105 @@
+#version 450
+
+// Analog Overshoot
+// by Astherix
+
+// adapted for slang from NTSC Codec (w/Overshoot & Noise) shadertoy
+// https://www.shadertoy.com/view/flG3zd
+
+// Licensed LGPLv3
+
+// This pass applies a simulation of analog overshoot, which
+// is the cause for ghosting artifacts around edges (sharp transitions)
+// This is not necessary for encoding/decoding.
+
+layout(push_constant) uniform Push
+{
+	vec4 SourceSize;
+	vec4 OriginalSize;
+	vec4 OutputSize;
+	uint FrameCount;
+	float hermite_tension, hermite_bias, decode_chroma_luma_separately;
+} params;
+
+// These two define the tension and bias parameters
+// of the Hermite interpolation function
+// Values closer to 0.5 on both parameters yield
+// more aggressive ghosting artifacts
+#pragma parameter hermite_tension "Hermite Tension" 0.25 0.01 1.0 0.01
+#pragma parameter hermite_bias "Hermite Bias" 0.75 0.01 1.0 0.01
+
+#pragma parameter decode_chroma_luma_separately "Decode Chroma and Luma Separately" 1.0 0.0 1.0 1.0
+#define DECODE_CHROMA_LUMA_SEPARATELY params.decode_chroma_luma_separately
+
+#define HERMITE_TENSION params.hermite_tension
+#define HERMITE_BIAS params.hermite_bias
+
+#define iChannel0 Source
+#define iResolution params.OutputSize.xy
+#define fragCoord (vTexCoord.xy * params.OutputSize.xy)
+#define fragColor FragColor
+#define iFrame params.FrameCount
+#define iTime (params.FrameCount / 60)
+
+layout(std140, set = 0, binding = 0) uniform UBO
+{
+	mat4 MVP;
+} global;
+
+#pragma stage vertex
+layout(location = 0) in vec4 Position;
+layout(location = 1) in vec2 TexCoord;
+layout(location = 0) out vec2 vTexCoord;
+
+void main()
+{
+   gl_Position = global.MVP * Position;
+   vTexCoord = TexCoord * 1.0001;
+}
+
+#pragma stage fragment
+layout(location = 0) in vec2 vTexCoord;
+layout(location = 0) out vec4 FragColor;
+layout(set = 0, binding = 2) uniform sampler2D Source;
+
+float hermite(float y0, float y1, float y2, float y3, float m, float tension, float bias) {
+    float m2 = m*m,
+          m3 = m2*m,
+          m0 =      (y1-y0)*(1.0+bias)*(1.0-tension)/2.0;
+          m0 = m0 + (y2-y1)*(1.0-bias)*(1.0-tension)/2.0;
+    float m1 =      (y2-y1)*(1.0+bias)*(1.0-tension)/2.0;
+          m1 = m1 + (y3-y2)*(1.0-bias)*(1.0-tension)/2.0;
+    float a0 =  2.0*m3 - 3.0*m2 + 1.0,
+          a1 =      m3 - 2.0*m2 + m,
+          a2 =      m3 -     m2,
+          a3 = -2.0*m3 + 3.0*m2;
+     
+     return (a0*y1+a1*m0+a2*m1+a3*y2);
+}
+
+void main()
+{
+   vec2 px = vTexCoord.xy * params.OutputSize.zw;
+    // Normalized pixel coordinates (from 0 to 1)
+    vec2 fcm1 = vec2(fragCoord.x-4.0, fragCoord.y)/iResolution.xy,
+         fcm0 = vec2(fragCoord.x-0.0, fragCoord.y)/iResolution.xy,
+         fcp1 = vec2(fragCoord.x+4.0, fragCoord.y)/iResolution.xy,
+         fcp2 = vec2(fragCoord.x+8.0, fragCoord.y)/iResolution.xy;
+    
+    vec3 y0 = texture(Source, fcm1).xyz,
+         y1 = texture(Source, fcm0).xyz,
+         y2 = texture(Source, fcp1).xyz,
+         y3 = texture(Source, fcp2).xyz;
+    
+    vec3 o = y1;
+         
+    float l = HERMITE_TENSION, y = HERMITE_BIAS;
+         
+    vec3 f = vec3(
+        hermite(y0.x, y1.x, y2.x, y3.x, l, y, y * 50.0),
+        hermite(y0.y, y1.y, y2.y, y3.y, l, y, y * 50.0),
+        hermite(y0.z, y1.z, y2.z, y3.z, l, y, y * 50.0)
+    );
+    
+    fragColor = mix(vec4(f, 1.0), vec4(y1, 1.0), DECODE_CHROMA_LUMA_SEPARATELY);
+}