Create frs_rcas.fsh

Add AMD FSR1

Author: Benjamin-Wegener

assets/shaders/frs_rcas.fsh

@@ -0,0 +1,117 @@
+// MIT License
+//
+// Copyright (c) 2021 Advanced Micro Devices, Inc. All rights reserved.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// Set precision for OpenGL ES
+#ifdef GL_ES
+precision mediump float;
+precision mediump int;
+#endif
+
+// Texture sampler for input image
+uniform sampler2D sampler0;
+
+// Texture coordinate delta (1.0 / viewport size)
+uniform vec2 u_texelDelta;
+
+// User settings:
+// u_setting.x = sharpness value (0.0 to 1.0)
+uniform vec4 u_setting;
+
+// Interpolated texture coordinates from vertex shader
+varying vec2 v_texcoord0;
+
+// Split-screen divider width for comparison views
+const float lineWidth = 0.005;
+
+// Luminance coefficients based on Rec. 709 standard
+// Used for converting RGB to perceptually weighted luminance
+const vec3 lumCoef = vec3(0.2126, 0.7152, 0.0722);
+
+// RCAS (Robust Contrast Adaptive Sharpening) constants
+// Peak negative lobe strength and its inverse
+const float rcasPeak = 8.0 - 3.0;      // Peak negative lobe strength
+const float rcasInvPeak = 1.0 / rcasPeak; // Inverse of peak strength
+
+// Small epsilon value for numerical stability
+// Matches AMD's reference implementation
+const float FSR_EPS = 0.0001;
+
+// Cross-shaped sampling pattern offsets (N, W, E, S)
+// Used for 4-tap cross sampling around center pixel
+const vec2 crossOffsets[4] = vec2[4](
+    vec2( 0.0, -1.0),  // North
+    vec2(-1.0,  0.0),  // West
+    vec2( 1.0,  0.0),  // East
+    vec2( 0.0,  1.0)   // South
+);
+
+// Vanilla RCAS kernel implementation (no edge-aware weighting)
+// Performs contrast adaptive sharpening on the input texture
+vec4 FsrRcasVanilla(vec2 uv) {
+    // Sample center pixel and convert to luminance
+    vec3 C = texture2D(sampler0, uv).rgb;
+    float CL = dot(C, lumCoef);
+
+    // Sample the 4 cross neighbors and convert to luminance
+    vec3 N = texture2D(sampler0, uv + crossOffsets[0] * u_texelDelta).rgb;  // North
+    vec3 W = texture2D(sampler0, uv + crossOffsets[1] * u_texelDelta).rgb;  // West
+    vec3 E = texture2D(sampler0, uv + crossOffsets[2] * u_texelDelta).rgb;  // East
+    vec3 S = texture2D(sampler0, uv + crossOffsets[3] * u_texelDelta).rgb;  // South
+
+    float NL = dot(N, lumCoef);  // North luminance
+    float WL = dot(W, lumCoef);  // West luminance
+    float EL = dot(E, lumCoef);  // East luminance
+    float SL = dot(S, lumCoef);  // South luminance
+
+    // Calculate adaptive amplification factor to prevent oversharpening
+    // Uses min/max range analysis to determine safe sharpening strength
+    vec3 minRGB = min(min(min(N, W), min(E, S)), C);  // Minimum RGB in 5-tap neighborhood
+    vec3 maxRGB = max(max(max(N, W), max(E, S)), C);  // Maximum RGB in 5-tap neighborhood
+    vec3 invMax = 1.0 / (maxRGB + FSR_EPS);          // Inverse of maximum (with epsilon)
+    vec3 amp = clamp(min(minRGB, 2.0 - maxRGB) * invMax, 0.0, 1.0);  // Amplification factor
+    amp = inversesqrt(amp + FSR_EPS);                // Inverse square root for non-linearity
+
+    // Calculate sharpening weight based on amplification
+    float w = -rcasInvPeak / dot(amp, lumCoef);
+
+    // Compute sharpened luminance using contrast adaptive formula
+    float sumL = NL + WL + EL + SL;                 // Sum of neighbor luminances
+    float invDen = 1.0 / (4.0 * w + 1.0);           // Inverse denominator
+    float sharpL = clamp((sumL * w + CL) * invDen, 0.0, 1.0);  // Sharpened luminance
+
+    // Reconstruct color by preserving chroma (hue/saturation)
+    // This prevents color shifts during sharpening
+    vec3 chroma = C - vec3(CL);                      // Extract chroma (color without brightness)
+    vec3 sharpColor = chroma + vec3(sharpL);        // Apply sharpened luminance to chroma
+
+    // Blend between original and sharpened based on user sharpness setting
+    // u_setting.x controls the blend: 0.0 = original, 1.0 = fully sharpened
+    vec3 outColor = mix(C, sharpColor, u_setting.x);
+    
+    return vec4(outColor, 1.0);
+}
+
+// Main fragment shader entry point
+void main() {
+    // Apply RCAS sharpening to the current fragment
+    gl_FragColor = FsrRcasVanilla(v_texcoord0);
+}