--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/shaders/bandlimit_pixel.f.glsl	Sun Apr 28 23:22:37 2024 -0700
@@ -0,0 +1,149 @@
+/*
+ * Bandlimited pixel footprint shader.
+ * Author: Themaister
+ * License: MIT
+ * Adapted from: https://github.com/Themaister/Granite/blob/master/assets/shaders/inc/bandlimited_pixel_filter.h
+ * ported to blastem shader format by hunterk
+ */
+
+// sensible values between 0.0 and 5.0
+#define SMOOTHNESS 0.5
+ 
+uniform sampler2D textures[2];
+uniform highp vec2 texsize;
+
+varying highp vec2 texcoord;
+
+// The cosine filter convolved with rect has a support of 0.5 + d pixels.
+// We can sample 4x4 regions, so we can deal with 2.0 pixel range in our filter,
+// and the maximum extent value we can have is 1.5.
+const highp float maximum_support_extent = 1.5;
+
+struct BandlimitedPixelInfo
+{
+	highp vec2 uv0;
+	highp vec2 uv1;
+	highp vec2 uv2;
+	highp vec2 uv3;
+	mediump vec4 weights;
+	mediump float l;
+};
+
+// Our Taylor approximation is not exact, normalize so the peak is 1.
+const highp float taylor_pi_half = 1.00452485553;
+const highp float taylor_normalization = 1.0 / taylor_pi_half;
+const highp float PI = 3.14159265359;
+const highp float PI_half = 0.5 * PI;
+
+#define gen_taylor(T) \
+mediump T taylor_sin(mediump T p) \
+{ \
+	mediump T p2 = p * p; \
+	mediump T p3 = p * p2; \
+	mediump T p5 = p2 * p3; \
+	return clamp(taylor_normalization * (p - p3 * (1.0 / 6.0) + p5 * (1.0 / 120.0)), -1.0, 1.0); \
+}
+// No templates in GLSL. Stamp out macros.
+gen_taylor(float)
+gen_taylor(vec2)
+gen_taylor(vec3)
+gen_taylor(vec4)
+
+// Given weights, compute a bilinear filter which implements the weight.
+// All weights are known to be non-negative, and separable.
+mediump vec3 compute_uv_phase_weight(mediump vec2 weights_u, mediump vec2 weights_v)
+{
+	// The sum of a bilinear sample has combined weight of 1, we will need to adjust the resulting sample
+	// to match our actual weight sum.
+	mediump float w = dot(weights_u.xyxy, weights_v.xxyy);
+	mediump float x = weights_u.y / max(weights_u.x + weights_u.y, 0.001);
+	mediump float y = weights_v.y / max(weights_v.x + weights_v.y, 0.001);
+	return vec3(x, y, w);
+}
+
+BandlimitedPixelInfo compute_pixel_weights(vec2 uv, vec2 size, vec2 inv_size)
+{
+	// Get derivatives in texel space.
+	// Need a non-zero derivative.
+	vec2 extent = max(fwidth(uv) * size * (SMOOTHNESS + 0.5), 1.0 / 256.0);
+
+	// Get base pixel and phase, range [0, 1).
+	vec2 pixel = uv * size - 0.5;
+	vec2 base_pixel = floor(pixel);
+	vec2 phase = pixel - base_pixel;
+
+	BandlimitedPixelInfo info;
+
+	mediump vec2 inv_extent = 1.0 / extent;
+	if (any(greaterThan(extent, vec2(maximum_support_extent))))
+	{
+		// We need to just do regular minimization filtering.
+		info = BandlimitedPixelInfo(vec2(0.0), vec2(0.0), vec2(0.0), vec2(0.0),
+		                            vec4(0.0, 0.0, 0.0, 0.0), 0.0);
+	}
+	else if (all(lessThanEqual(extent, vec2(0.5))))
+	{
+		// We can resolve the filter by just sampling a single 2x2 block.
+		mediump vec2 shift = 0.5 + 0.5 * taylor_sin(PI_half * clamp(inv_extent * (phase - 0.5), -1.0, 1.0));
+		info = BandlimitedPixelInfo((base_pixel + 0.5 + shift) * inv_size, vec2(0.0), vec2(0.0), vec2(0.0),
+		                            vec4(1.0, 0.0, 0.0, 0.0), 1.0);
+	}
+	else
+	{
+		// Full 4x4 sampling.
+
+		// Fade between bandlimited and normal sampling.
+		// Fully use bandlimited filter at LOD 0, normal filtering at approx. LOD -0.5.
+		mediump float max_extent = max(extent.x, extent.y);
+		mediump float l = clamp(1.0 - (max_extent - 1.0) / (maximum_support_extent - 1.0), 0.0, 1.0);
+
+		mediump vec4 sine_phases_x = PI_half * clamp(inv_extent.x * (phase.x + vec4(1.5, 0.5, -0.5, -1.5)), -1.0, 1.0);
+		mediump vec4 sines_x = taylor_sin(sine_phases_x);
+
+		mediump vec4 sine_phases_y = PI_half * clamp(inv_extent.y * (phase.y + vec4(1.5, 0.5, -0.5, -1.5)), -1.0, 1.0);
+		mediump vec4 sines_y = taylor_sin(sine_phases_y);
+
+		mediump vec2 sine_phases_end = PI_half * clamp(inv_extent * (phase - 2.5), -1.0, 1.0);
+		mediump vec2 sines_end = taylor_sin(sine_phases_end);
+
+		mediump vec4 weights_x = 0.5 * (sines_x - vec4(sines_x.yzw, sines_end.x));
+		mediump vec4 weights_y = 0.5 * (sines_y - vec4(sines_y.yzw, sines_end.y));
+
+		mediump vec3 w0 = compute_uv_phase_weight(weights_x.xy, weights_y.xy);
+		mediump vec3 w1 = compute_uv_phase_weight(weights_x.zw, weights_y.xy);
+		mediump vec3 w2 = compute_uv_phase_weight(weights_x.xy, weights_y.zw);
+		mediump vec3 w3 = compute_uv_phase_weight(weights_x.zw, weights_y.zw);
+
+		info = BandlimitedPixelInfo((base_pixel - 0.5 + w0.xy) * inv_size,
+									(base_pixel + vec2(1.5, -0.5) + w1.xy) * inv_size,
+									(base_pixel + vec2(-0.5, 1.5) + w2.xy) * inv_size,
+									(base_pixel + 1.5 + w3.xy) * inv_size,
+									vec4(w0.z, w1.z, w2.z, w3.z), l);
+	}
+
+	return info;
+}
+
+mediump vec4 sample_bandlimited_pixel(sampler2D samp, vec2 uv, BandlimitedPixelInfo info, float lod)
+{
+	mediump vec4 color = texture2D(samp, uv);
+	if (info.l > 0.0)
+	{
+		mediump vec4 bandlimited = info.weights.x * pow(texture2D(samp, info.uv0, lod), vec4(2.2));
+		if (info.weights.x < 1.0)
+		{
+			bandlimited += info.weights.y * pow(texture2D(samp, info.uv1, lod), vec4(2.2));
+			bandlimited += info.weights.z * pow(texture2D(samp, info.uv2, lod), vec4(2.2));
+			bandlimited += info.weights.w * pow(texture2D(samp, info.uv3, lod), vec4(2.2));
+		}
+		color = mix(color, bandlimited, info.l);
+	}
+	return color;
+}
+
+void main()
+{
+	BandlimitedPixelInfo info = compute_pixel_weights(texcoord, texsize.xy, 1.0 / texsize.xy);
+	mediump vec3 result = sample_bandlimited_pixel(textures[0], texcoord, info, 0.0).rgb;
+	gl_FragColor = vec4(sqrt(clamp(result, 0.0, 1.0)), 1.0);
+}
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