From cc906c83cdf896d94b7ccf91258466714be631f6 Mon Sep 17 00:00:00 2001
From: Nick Senger <dev@nsenger.com>
Date: Wed, 8 Nov 2023 19:12:53 -0800
Subject: feat: quad shadows

---
 wgpu/src/shader/quad.wgsl       | 18 +++++++-----------
 wgpu/src/shader/quad/solid.wgsl | 36 +++++++++++++++++++++++++++++++-----
 2 files changed, 38 insertions(+), 16 deletions(-)

(limited to 'wgpu/src/shader')

diff --git a/wgpu/src/shader/quad.wgsl b/wgpu/src/shader/quad.wgsl
index f919cfe2..4de73362 100644
--- a/wgpu/src/shader/quad.wgsl
+++ b/wgpu/src/shader/quad.wgsl
@@ -11,19 +11,15 @@ fn distance_alg(
     size: vec2<f32>,
     radius: f32
 ) -> f32 {
-    var inner_size: vec2<f32> = size - vec2<f32>(radius, radius) * 2.0;
+    var inner_half_size: vec2<f32> = (size - vec2<f32>(radius, radius) * 2.0) / 2.0;
     var top_left: vec2<f32> = position + vec2<f32>(radius, radius);
-    var bottom_right: vec2<f32> = top_left + inner_size;
-
-    var top_left_distance: vec2<f32> = top_left - frag_coord;
-    var bottom_right_distance: vec2<f32> = frag_coord - bottom_right;
-
-    var dist: vec2<f32> = vec2<f32>(
-        max(max(top_left_distance.x, bottom_right_distance.x), 0.0),
-        max(max(top_left_distance.y, bottom_right_distance.y), 0.0)
-    );
+    return rounded_box_sdf(frag_coord - top_left - inner_half_size, inner_half_size, 0.0);
+}
 
-    return sqrt(dist.x * dist.x + dist.y * dist.y);
+// Given a vector from a point to the center of a rounded rectangle of the given `size` and
+// border `radius`, determines the point's distance from the nearest edge of the rounded rectangle
+fn rounded_box_sdf(to_center: vec2<f32>, size: vec2<f32>, radius: f32) -> f32 {
+    return length(max(abs(to_center) - size + vec2<f32>(radius, radius), vec2<f32>(0.0, 0.0))) - radius;
 }
 
 // Based on the fragement position and the center of the quad, select one of the 4 radi.
diff --git a/wgpu/src/shader/quad/solid.wgsl b/wgpu/src/shader/quad/solid.wgsl
index f84dd7ab..cb4a3816 100644
--- a/wgpu/src/shader/quad/solid.wgsl
+++ b/wgpu/src/shader/quad/solid.wgsl
@@ -6,6 +6,9 @@ struct SolidVertexInput {
     @location(3) border_color: vec4<f32>,
     @location(4) border_radius: vec4<f32>,
     @location(5) border_width: f32,
+    @location(6) shadow_color: vec4<f32>,
+    @location(7) shadow_offset: vec2<f32>,
+    @location(8) shadow_blur_radius: f32,
 }
 
 struct SolidVertexOutput {
@@ -16,14 +19,19 @@ struct SolidVertexOutput {
     @location(3) scale: vec2<f32>,
     @location(4) border_radius: vec4<f32>,
     @location(5) border_width: f32,
+    @location(6) shadow_color: vec4<f32>,
+    @location(7) shadow_offset: vec2<f32>,
+    @location(8) shadow_blur_radius: f32,
 }
 
 @vertex
 fn solid_vs_main(input: SolidVertexInput) -> SolidVertexOutput {
     var out: SolidVertexOutput;
 
-    var pos: vec2<f32> = input.pos * globals.scale;
-    var scale: vec2<f32> = input.scale * globals.scale;
+    var pos: vec2<f32> = (input.pos + min(input.shadow_offset, vec2<f32>(0.0, 0.0)) - input.shadow_blur_radius) * globals.scale;
+    var quad_pos: vec2<f32> = input.pos * globals.scale;
+    var scale: vec2<f32> = (input.scale + vec2<f32>(abs(input.shadow_offset.x), abs(input.shadow_offset.y)) + input.shadow_blur_radius * 2.0) * globals.scale;
+    var quad_scale: vec2<f32> = input.scale * globals.scale;
 
     var min_border_radius = min(input.scale.x, input.scale.y) * 0.5;
     var border_radius: vec4<f32> = vec4<f32>(
@@ -43,10 +51,13 @@ fn solid_vs_main(input: SolidVertexInput) -> SolidVertexOutput {
     out.position = globals.transform * transform * vec4<f32>(vertex_position(input.vertex_index), 0.0, 1.0);
     out.color = input.color;
     out.border_color = input.border_color;
-    out.pos = pos;
-    out.scale = scale;
+    out.pos = quad_pos;
+    out.scale = quad_scale;
     out.border_radius = border_radius * globals.scale;
     out.border_width = input.border_width * globals.scale;
+    out.shadow_color = input.shadow_color;
+    out.shadow_offset = input.shadow_offset * globals.scale;
+    out.shadow_blur_radius = input.shadow_blur_radius * globals.scale;
 
     return out;
 }
@@ -95,5 +106,20 @@ fn solid_fs_main(
         dist
     );
 
-    return vec4<f32>(mixed_color.x, mixed_color.y, mixed_color.z, mixed_color.w * radius_alpha);
+    let quad_color = vec4<f32>(mixed_color.x, mixed_color.y, mixed_color.z, mixed_color.w * radius_alpha);
+
+    if input.shadow_color.a > 0.0 {
+        let shadow_distance = rounded_box_sdf(input.position.xy - input.pos - input.shadow_offset - (input.scale / 2.0), input.scale / 2.0, border_radius);
+        let shadow_alpha = 1.0 - smoothstep(-input.shadow_blur_radius, input.shadow_blur_radius, shadow_distance);
+        let shadow_color = input.shadow_color;
+        let base_color = select(
+            vec4<f32>(shadow_color.x, shadow_color.y, shadow_color.z, 0.0),
+            quad_color,
+            quad_color.a > 0.0
+        );
+
+        return mix(base_color, shadow_color, (1.0 - radius_alpha) * shadow_alpha);
+    } else {
+        return quad_color;
+    }
 }
-- 
cgit