What if we just rely entirely on SGSR common than using EdgeDir?

src/video_core/host_shaders/sgsr1_shader_mobile.frag

@@ -6,9 +6,9 @@
 precision highp float;
 precision highp int;
 
-// Operation modes: RGBA -> 1, RGBY -> 3, LERP -> 4
-#define OPERATION_MODE 1
 #define EDGE_THRESHOLD (8.0 / 255.0)
+#define DIRECTION_EPSILON 6.5e-05
+#define DEVIATION_FLOOR 6.0e-02
 
 layout(push_constant) uniform constants {
     vec2 scale;
@@ -21,20 +21,37 @@ layout(set = 0, binding = 0) uniform sampler2D sampler0;
 layout(location=0) in vec2 texcoord;
 layout(location=0) out vec4 frag_color;
 
-vec4 weightY(vec4 dx, vec4 dy, vec4 std) {
-    vec4 x = ((dx * dx) + (dy * dy)) * 0.55f + std;
-    return (x - 1.f) * (x - 4.f) * 3.8125f; // approx. of (x - 1) * (x - 4)^3
+mediump vec4 fastLanczos2(mediump vec4 x) {
+    mediump vec4 wA = x - 4.0f;
+    mediump vec4 wB = x * wA - wA;
+    wA *= wA;
+    return wB * wA;
+}
+
+mediump vec2 edgeDirection(mediump vec4 left, mediump vec4 right) {
+    mediump float RxLz = right.x - left.z;
+    mediump float RwLy = right.w - left.y;
+    mediump vec2 delta = vec2(RxLz + RwLy, RxLz - RwLy);
+    mediump float length_inv =
+        inversesqrt((delta.x * delta.x + DIRECTION_EPSILON) + delta.y * delta.y);
+    return delta * length_inv;
+}
+
+mediump vec4 weightY(mediump vec4 dx, mediump vec4 dy, mediump vec4 c, mediump float std,
+                     mediump vec2 dir) {
+    mediump vec4 edge_dis = dx * dir.y + dy * dir.x;
+    mediump vec4 x = (dx * dx + dy * dy) +
+                     (edge_dis * edge_dis) * (clamp((c * c) * std, 0.0f, 1.0f) * 0.7f - 1.0f);
+    return fastLanczos2(x);
 }
 
 void main() {
-    vec4 color = textureLod(sampler0, texcoord.xy, 0.0f);
-    // image coord
-    vec2 icoord = (texcoord * size + vec2(-0.5f, 0.5f));
-    vec2 icoord_pixel = floor(icoord);
-    vec2 coord = icoord_pixel * scale;
-    vec2 pl = icoord - icoord_pixel;
-    // left: 0, right: 1, upDown: 2
-    mat3x4 dg = mat3x4(
+    mediump vec4 color = textureLod(sampler0, texcoord.xy, 0.0f);
+    highp vec2 icoord = (texcoord * size + vec2(-0.5f, 0.5f));
+    highp vec2 icoord_pixel = floor(icoord);
+    highp vec2 coord = icoord_pixel * scale;
+    mediump vec2 pl = icoord - icoord_pixel;
+    mediump mat3x4 dg = mat3x4(
         textureGather(sampler0, coord, 1),
         textureGather(sampler0, coord + vec2(2.f * scale.x, 0.0f), 1),
         vec4(
@@ -42,42 +59,40 @@ void main() {
             textureGather(sampler0, coord + vec2(scale.x, +scale.y), 1).yx
         )
     );
-    float edgeVote = abs(dg[0].z - dg[0].y) + abs(color.y - dg[0].y) + abs(color.y - dg[0].z);
+    mediump float edgeVote =
+        abs(dg[0].z - dg[0].y) + abs(color.y - dg[0].y) + abs(color.y - dg[0].z);
     if (edgeVote > EDGE_THRESHOLD) {
-        float mean = (dg[0].y + dg[0].z + dg[1].x + dg[1].w) * 0.25f;
+        mediump float mean = (dg[0].y + dg[0].z + dg[1].x + dg[1].w) * 0.25f;
         dg = dg - mean;
-        vec4 sum = abs(dg[0]) + abs(dg[1]) + abs(dg[2]);
-        float std = 2.181818f / (sum.x + sum.y + sum.z + sum.w);
-        mat2x4 w = mat2x4(
-            weightY(
-                pl.xxxx + vec4(+1.0f, +0.0f, +0.0f, +1.0f),
-                pl.yyyy + vec4(-1.0f, -1.0f, +0.0f, +0.0f),
-                clamp(abs(dg[0]) * std, 0.0f, 1.0f)
-            ) + weightY(
-                pl.xxxx + vec4(-1.0f, -2.0f, -2.0f, -1.0f),
-                pl.yyyy + vec4(-1.0f, -1.0f, +0.0f, +0.0f),
-                clamp(abs(dg[1]) * std, 0.0f, 1.0f)
-            ) + weightY(
-                pl.xxxx + vec4(+0.0f, -1.0f, -1.0f, +0.0f),
-                pl.yyyy + vec4(+1.0f, +1.0f, -2.0f, -2.0f),
-                clamp(abs(dg[2]) * std, 0.0f, 1.0f)
-            ),
-            dg[0] + dg[1] + dg[2]
+        mediump float sum = dot(abs(dg[0]) + abs(dg[1]) + abs(dg[2]), vec4(1.0f));
+        mediump float sum_mean = 1.014185e+01f / max(sum, DEVIATION_FLOOR);
+        mediump float std = sum_mean * sum_mean;
+        mediump vec2 dir = edgeDirection(dg[0], dg[1]);
+        mediump vec4 w0 = weightY(
+            pl.xxxx + vec4(+1.0f, +0.0f, +0.0f, +1.0f),
+            pl.yyyy + vec4(-1.0f, -1.0f, +0.0f, +0.0f),
+            dg[0], std, dir
+        );
+        mediump vec4 w1 = weightY(
+            pl.xxxx + vec4(-1.0f, -2.0f, -2.0f, -1.0f),
+            pl.yyyy + vec4(-1.0f, -1.0f, +0.0f, +0.0f),
+            dg[1], std, dir
         );
-        // compute final y with bounds
-        vec2 yb = vec2(
-            min(min(dg[0].y, dg[0].z), min(dg[1].x, dg[1].w)), // min
-            max(max(dg[0].y, dg[0].z), max(dg[1].x, dg[1].w))  // max
+        mediump vec4 w2 = weightY(
+            pl.xxxx + vec4(+0.0f, -1.0f, -1.0f, +0.0f),
+            pl.yyyy + vec4(+1.0f, +1.0f, -2.0f, -2.0f),
+            dg[2], std, dir
         );
-        vec2 fvy = vec2(
-            w[0].x + w[0].y + w[0].z + w[0].w,
-            w[1].x + w[1].y + w[1].z + w[1].w
+        mediump float sum_w = dot(w0 + w1 + w2, vec4(1.0f));
+        mediump float sum_wc = dot(w0 * dg[0] + w1 * dg[1] + w2 * dg[2], vec4(1.0f));
+        mediump vec2 yb = vec2(
+            min(min(dg[0].y, dg[0].z), min(dg[1].x, dg[1].w)),
+            max(max(dg[0].y, dg[0].z), max(dg[1].x, dg[1].w))
         );
-        float fy = clamp((fvy.y / fvy.x) * edge_sharpness, yb[0], yb[1]);
-        // Smooth high contrast input
-        float dy = clamp(fy - color.y + mean, -23.0f / 255.0f, 23.0f / 255.0f);
+        mediump float fy = clamp((sum_wc / sum_w) * edge_sharpness, yb[0], yb[1]);
+        mediump float dy = clamp(fy - color.y + mean, -23.0f / 255.0f, 23.0f / 255.0f);
         color = clamp(color + dy, 0.0f, 1.0f);
     }
-    color.w = 1.0f;  //assume alpha channel is not used
+    color.w = 1.0f;
     frag_color.xyzw = color;
-}
+}