From 5fc0d5396b7ce338f74baa33c71353e265bf0552 Mon Sep 17 00:00:00 2001
From: gizmo98 <atz.SE@gmx.de>
Date: Thu, 4 May 2023 20:10:58 +0200
Subject: [PATCH] Add uniform-nearest shader

Features:
- produces nearest neighbor look with fractional scales.
- uses texture AA shader code.
- uses hotizontal subpixel scaling.
- due to different pixel sizes, moving sprites change dimension if nearest neighbor is used with fractional scaling. This looks unsteady. This shader uniforms pixel dimensions. Output looks much quieter.

https://forums.libretro.com/t/uniform-nearest-interpolation-shader/41492
---
 interpolation/shaders/uniform-nearest.slang | 125 ++++++++++++++++++++
 interpolation/uniform-nearest.slangp        |   8 ++
 2 files changed, 133 insertions(+)
 create mode 100644 interpolation/shaders/uniform-nearest.slang
 create mode 100644 interpolation/uniform-nearest.slangp

diff --git a/interpolation/shaders/uniform-nearest.slang b/interpolation/shaders/uniform-nearest.slang
new file mode 100644
index 0000000..0c2025f
--- /dev/null
+++ b/interpolation/shaders/uniform-nearest.slang
@@ -0,0 +1,125 @@
+#version 450
+/* 
+ * gizmo98 uniform-nearest shader
+ * Copyright (C) 2023 gizmo98
+ *
+ *   This program is free software; you can redistribute it and/or modify it
+ *   under the terms of the GNU General Public License as published by the Free
+ *   Software Foundation; either version 2 of the License, or (at your option)
+ *   any later version.
+ *
+ * version 0.1, 28.04.2023
+ * ---------------------------------------------------------------------------------------
+ * - initial commit
+ * 
+ * https://github.com/gizmo98/gizmo-crt-shader
+ *
+ * This shader texture AA shader code and subpixel scaling to produce a nearest neighbor
+ * look with even placed pixels. If nearest neighbor is applied to fractional scaled output 
+ * pixels look uneven and moving sprites change dimension which looks ugly.
+ *
+ * BGR_LCD_PATTERN most LCDs have a RGB pixel pattern. Enable BGR pattern with this switch
+ *
+ * uses parts of texture anti-aliasing shader from Ikaros https://www.shadertoy.com/view/ldsSRX
+ */
+
+layout(push_constant) uniform Push
+{
+	vec4 SourceSize;
+	vec4 OriginalSize;
+	vec4 OutputSize;
+	uint FrameCount;
+	float BGR_LCD_PATTERN;
+} params;
+
+layout(std140, set = 0, binding = 0) uniform UBO
+{
+	mat4 MVP;
+} global;
+
+#pragma parameter BGR_LCD_PATTERN "BGR output pattern"         0.0 0.0 1.0 1.0
+
+#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;
+}
+
+#pragma stage fragment
+layout(location = 0) in vec2 vTexCoord;
+layout(location = 0) out vec4 FragColor;
+layout(set = 0, binding = 2) uniform sampler2D Source;
+
+vec2 saturateA(in vec2 x)
+{
+    return clamp(x, 0.0, 1.0);
+}
+
+vec2 magnify(in vec2 uv, in vec2 res)
+{
+    uv *= res; 
+    return (saturateA(fract(uv) / saturateA(fwidth(uv))) + floor(uv) - 0.5) / res.xy;
+}
+
+vec4 textureAA(in vec2 uv){
+    vec2 texSize = vec2(textureSize(Source, 0));
+    uv = magnify(uv,texSize.xy);
+    uv = uv*texSize.xy + 0.5;
+
+    vec2 iuv = floor(uv);
+    vec2 fuv = uv - iuv;    
+    uv = vec2(uv + vec2(-0.5,-0.5)) / texSize.xy;
+    return texture( Source, uv );
+}
+
+vec4 textureSubpixelScaling(in vec2 uvr, in vec2 uvg, in vec2 uvb ){
+    return vec4(textureAA(uvr).r, textureAA(uvg).g, textureAA(uvb).b, 1.0);
+}
+
+float GetFuv(in vec2 uv){
+    vec2 texSize = vec2(textureSize(Source, 0));
+    uv = uv*texSize.xy + 0.5;
+    vec2 iuv = floor(uv);
+    vec2 fuv = uv - iuv;
+    return abs((fuv*fuv*fuv*(fuv*(fuv*6.0-15.0)+10.0)).y - 0.5);
+}
+
+vec3 XCoords(in float coord, in float factor){
+    float iGlobalTime = float(params.FrameCount)*0.025;
+    float spread = 0.333;
+    vec3 coords = vec3(coord);
+    if(params.BGR_LCD_PATTERN == 1.0)
+        coords.r += spread * 2.0;
+    else
+        coords.b += spread * 2.0;
+    coords.g += spread;
+    coords *= factor;
+    return coords;
+}
+
+float YCoord(in float coord, in float factor){
+    return coord * factor;
+}
+
+void main()
+{
+    vec2 texSize = vec2(textureSize(Source, 0));
+    vec2 texcoord = vTexCoord.xy;
+
+    vec2 fragCoord = texcoord.xy * params.OutputSize.xy;
+
+    vec2 factor = texSize.xy / params.OutputSize.xy ;
+    highp float yCoord = YCoord(fragCoord.y, factor.y) ;
+    highp vec3 xCoords = XCoords(fragCoord.x, factor.x) ;
+
+    vec2 coord_r = vec2(xCoords.r/ texSize.x, texcoord.y) ;
+    vec2 coord_g = vec2(xCoords.g, yCoord) / texSize.xy;
+    vec2 coord_b = vec2(xCoords.b, yCoord) / texSize.xy;
+
+    FragColor = textureSubpixelScaling(coord_r,coord_g,coord_b);
+}
diff --git a/interpolation/uniform-nearest.slangp b/interpolation/uniform-nearest.slangp
new file mode 100644
index 0000000..ba2b8ee
--- /dev/null
+++ b/interpolation/uniform-nearest.slangp
@@ -0,0 +1,8 @@
+shaders = "1"
+shader0 = "shaders/uniform-nearest.slang"
+filter_linear0 = "true"
+scale_type0 = viewport
+
+parameters = "BGR_LCD_PATTERN"
+BGR_LCD_PATTERN = "0.0"
+