Merge pull request #46301 from Calinou/gles2-improve-shadow-rendering

Improve PCF13 shadow rendering in GLES2 by using a soft PCF filter

doc/classes/ProjectSettings.xml

@@ -1261,6 +1261,7 @@
 		</member>
 		<member name="rendering/quality/shadows/filter_mode" type="int" setter="" getter="" default="1">
 			Shadow filter mode. Higher-quality settings result in smoother shadows that flicker less when moving. "Disabled" is the fastest option, but also has the lowest quality. "PCF5" is smoother but is also slower. "PCF13" is the smoothest option, but is also the slowest.
+			[b]Note:[/b] When using the GLES2 backend, the "PCF13" option actually uses 16 samples to emulate linear filtering in the shader. This results in a shadow appearance similar to the one produced by the GLES3 backend.
 		</member>
 		<member name="rendering/quality/shadows/filter_mode.mobile" type="int" setter="" getter="" default="0">
 			Lower-end override for [member rendering/quality/shadows/filter_mode] on mobile devices, due to performance concerns or driver support.

drivers/gles2/shaders/scene.glsl

@@ -1434,24 +1434,47 @@ float sample_shadow(highp sampler2D shadow, highp vec4 spos) {
 
 #ifdef SHADOW_MODE_PCF_13
 
+	// Soft PCF filter adapted from three.js:
+	// https://github.com/mrdoob/three.js/blob/0c815022849389cbe6de14a93e1c2fc7e4b21c18/src/renderers/shaders/ShaderChunk/shadowmap_pars_fragment.glsl.js#L148-L182
+	// This method actually uses 16 shadow samples. This soft filter isn't needed in GLES3
+	// as we can use hardware-based linear filtering instead of emulating it in the shader
+	// like we're doing here.
 	spos.xyz /= spos.w;
 	vec2 pos = spos.xy;
 	float depth = spos.z;
-
-	float avg = SAMPLE_SHADOW_TEXEL(shadow, pos, depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(shadow_pixel_size.x, 0.0), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(-shadow_pixel_size.x, 0.0), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(0.0, shadow_pixel_size.y), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(0.0, -shadow_pixel_size.y), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(shadow_pixel_size.x, shadow_pixel_size.y), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(-shadow_pixel_size.x, shadow_pixel_size.y), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(shadow_pixel_size.x, -shadow_pixel_size.y), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(-shadow_pixel_size.x, -shadow_pixel_size.y), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(shadow_pixel_size.x * 2.0, 0.0), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(-shadow_pixel_size.x * 2.0, 0.0), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(0.0, shadow_pixel_size.y * 2.0), depth);
-	avg += SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(0.0, -shadow_pixel_size.y * 2.0), depth);
-	return avg * (1.0 / 13.0);
+	vec2 f = fract(pos * (1.0 / shadow_pixel_size) + 0.5);
+	pos -= f * shadow_pixel_size;
+
+	return (
+				   SAMPLE_SHADOW_TEXEL(shadow, pos, depth) +
+				   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(shadow_pixel_size.x, 0.0), depth) +
+				   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(0.0, shadow_pixel_size.y), depth) +
+				   SAMPLE_SHADOW_TEXEL(shadow, pos + shadow_pixel_size, depth) +
+				   mix(
+						   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(-shadow_pixel_size.x, 0.0), depth),
+						   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(2.0 * shadow_pixel_size.x, 0.0), depth),
+						   f.x) +
+				   mix(
+						   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(-shadow_pixel_size.x, shadow_pixel_size.y), depth),
+						   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(2.0 * shadow_pixel_size.x, shadow_pixel_size.y), depth),
+						   f.x) +
+				   mix(
+						   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(0.0, -shadow_pixel_size.y), depth),
+						   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(0.0, 2.0 * shadow_pixel_size.y), depth),
+						   f.y) +
+				   mix(
+						   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(shadow_pixel_size.x, -shadow_pixel_size.y), depth),
+						   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(shadow_pixel_size.x, 2.0 * shadow_pixel_size.y), depth),
+						   f.y) +
+				   mix(
+						   mix(SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(-shadow_pixel_size.x, -shadow_pixel_size.y), depth),
+								   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(2.0 * shadow_pixel_size.x, -shadow_pixel_size.y), depth),
+								   f.x),
+						   mix(SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(-shadow_pixel_size.x, 2.0 * shadow_pixel_size.y), depth),
+								   SAMPLE_SHADOW_TEXEL(shadow, pos + vec2(2.0 * shadow_pixel_size.x, 2.0 * shadow_pixel_size.y), depth),
+								   f.x),
+						   f.y)) *
+		   (1.0 / 9.0);
 #endif
 
 #ifdef SHADOW_MODE_PCF_5