add smootheststep shader

retro/shaders/smootheststep.slang

@@ -0,0 +1,62 @@
+#version 450
+
+/*
+	Fragment shader based on "Improved texture interpolation" by Iñigo Quílez
+	Original description: http://www.iquilezles.org/www/articles/texture/texture.htm
+*/
+
+layout(push_constant) uniform Push
+{
+	vec4 SourceSize;
+	vec4 OriginalSize;
+	vec4 OutputSize;
+	uint FrameCount;
+} params;
+
+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;
+}
+
+#pragma stage fragment
+layout(location = 0) in vec2 vTexCoord;
+layout(location = 0) out vec4 FragColor;
+layout(set = 0, binding = 2) uniform sampler2D Source;
+
+void main()
+{
+	vec2 p = vTexCoord.xy;
+
+	p = p * params.SourceSize.xy + vec2(0.5, 0.5);
+
+	vec2 i = floor(p);
+	vec2 f = p - i;
+
+	// Smoothstep - amazingly, smoothstep() is slower than calculating directly the expression!
+//	f = smoothstep(0.0, 1.0, f);
+//	f = f * f * ( -2.0 * f + 3.0);
+
+	// Quilez - This is sharper than smoothstep.
+	//f = f * f * f * (f * (f * 6.0 - vec2(15.0, 15.0)) + vec2(10.0, 10.0));
+
+	// smootheststep - This is even sharper than Quilez!
+	f = f * f * f * f * (f * (f * (-20.0 * f + vec2(70.0, 70.0)) - vec2(84.0, 84.0)) + vec2(35.0, 35.0));
+
+	p = i + f;
+
+	p = (p - vec2(0.5, 0.5)) * params.SourceSize.zw;
+
+	// final sum and weight normalization
+   FragColor = vec4(texture(Source, p).rgb, 1.0);
+}

retro/smootheststep.slangp

@@ -0,0 +1,4 @@
+shaders = 1
+
+shader0 = shaders/smootheststep.slang
+filter_linear0 = true