12 files changed, 72 insertions, 28 deletions

diff --git a/shaders/image.frag.glsl b/shaders/image.frag.glsl
index 2a3c2038..0cc1b2ee 100644
--- a/shaders/image.frag.glsl
+++ b/shaders/image.frag.glsl
@@ -1,6 +1,9 @@
 #version 450
 
 layout(set = 2, binding = 0) uniform sampler2D u_image;
+layout(std140, set = 3, binding = 0) uniform UiUniforms {
+    float background_opacity;
+} u_ui;
 
 layout(location = 0) in vec2 v_uv;
 layout(location = 1) in vec2 v_panel_uv;
@@ -19,6 +22,9 @@ float cellNoise(uint serial, uint col, uint row) {
 
 void main() {
     vec4 source = texture(u_image, v_uv);
+    // Keep source coverage for destination subtraction; the pipeline scales
+    // source alpha by the same opacity through its alpha blend constant.
+    source.rgb *= clamp(u_ui.background_opacity, 0.0, 1.0);
     uint effect = v_effect.x & 0x7fffffffu;
     bool oldLayer = (v_effect.x & 0x80000000u) != 0u;
     float progress = clamp(uintBitsToFloat(v_effect.y), 0.0, 1.0);
diff --git a/shaders/overlay.frag.glsl b/shaders/overlay.frag.glsl
index 86c0188b..b5ac8d5a 100644
--- a/shaders/overlay.frag.glsl
+++ b/shaders/overlay.frag.glsl
@@ -1,9 +1,17 @@
 #version 450
 
+layout(std140, set = 3, binding = 0) uniform UiUniforms {
+    float background_opacity;
+} u_ui;
+
 layout(location = 0) in vec4 v_color;
 
 layout(location = 0) out vec4 o_col;
 
 void main() {
-    o_col = v_color;
+    // Preserve shape coverage for destination subtraction. The pipeline uses
+    // the matching opacity blend constant for source alpha, so graphics laid
+    // over a background with the same opacity do not accumulate opaque seams.
+    // Text/cursor draw groups bind opacity 1 instead.
+    o_col = vec4(v_color.rgb * clamp(u_ui.background_opacity, 0.0, 1.0), v_color.a);
 }
diff --git a/shaders/prebuilt/image.frag.glsl b/shaders/prebuilt/image.frag.glsl
index 2a3c2038..0cc1b2ee 100644
--- a/shaders/prebuilt/image.frag.glsl
+++ b/shaders/prebuilt/image.frag.glsl
@@ -1,6 +1,9 @@
 #version 450
 
 layout(set = 2, binding = 0) uniform sampler2D u_image;
+layout(std140, set = 3, binding = 0) uniform UiUniforms {
+    float background_opacity;
+} u_ui;
 
 layout(location = 0) in vec2 v_uv;
 layout(location = 1) in vec2 v_panel_uv;
@@ -19,6 +22,9 @@ float cellNoise(uint serial, uint col, uint row) {
 
 void main() {
     vec4 source = texture(u_image, v_uv);
+    // Keep source coverage for destination subtraction; the pipeline scales
+    // source alpha by the same opacity through its alpha blend constant.
+    source.rgb *= clamp(u_ui.background_opacity, 0.0, 1.0);
     uint effect = v_effect.x & 0x7fffffffu;
     bool oldLayer = (v_effect.x & 0x80000000u) != 0u;
     float progress = clamp(uintBitsToFloat(v_effect.y), 0.0, 1.0);
diff --git a/shaders/prebuilt/image.frag.spv b/shaders/prebuilt/image.frag.spv
index ac6a2682..c9511ad7 100644
--- a/shaders/prebuilt/image.frag.spv
+++ b/shaders/prebuilt/image.frag.spv
diff --git a/shaders/prebuilt/overlay.frag.glsl b/shaders/prebuilt/overlay.frag.glsl
index 86c0188b..b5ac8d5a 100644
--- a/shaders/prebuilt/overlay.frag.glsl
+++ b/shaders/prebuilt/overlay.frag.glsl
@@ -1,9 +1,17 @@
 #version 450
 
+layout(std140, set = 3, binding = 0) uniform UiUniforms {
+    float background_opacity;
+} u_ui;
+
 layout(location = 0) in vec4 v_color;
 
 layout(location = 0) out vec4 o_col;
 
 void main() {
-    o_col = v_color;
+    // Preserve shape coverage for destination subtraction. The pipeline uses
+    // the matching opacity blend constant for source alpha, so graphics laid
+    // over a background with the same opacity do not accumulate opaque seams.
+    // Text/cursor draw groups bind opacity 1 instead.
+    o_col = vec4(v_color.rgb * clamp(u_ui.background_opacity, 0.0, 1.0), v_color.a);
 }
diff --git a/shaders/prebuilt/overlay.frag.spv b/shaders/prebuilt/overlay.frag.spv
index 59bbb9d4..e296e99e 100644
--- a/shaders/prebuilt/overlay.frag.spv
+++ b/shaders/prebuilt/overlay.frag.spv
diff --git a/shaders/prebuilt/ui.frag.glsl b/shaders/prebuilt/ui.frag.glsl
index 69cb63b9..3c366602 100644
--- a/shaders/prebuilt/ui.frag.glsl
+++ b/shaders/prebuilt/ui.frag.glsl
@@ -1,12 +1,16 @@
 #version 450
 
 // Sample the glyph atlas (R = coverage 0..1) and mix the cell's bg up to its fg
-// by that coverage. Output is PREMULTIPLIED: an opaque cell is unchanged, and a
-// cell whose background is the see-through ground (config.gui_transparent, a
-// theme with no bg of its own) contributes only its ink, at the ink's own
-// coverage, so the compositor keeps the rest.
+// by that coverage. Output is PREMULTIPLIED: an opaque cell is unchanged.
+// WindowOpacity changes only the ground's coverage, never the glyph's ink.
+// A cell whose background is the see-through ground (config.gui_transparent,
+// a theme with no bg of its own) still contributes only its ink, at the ink's
+// own coverage, so the compositor keeps the rest.
 
 layout(set = 2, binding = 0) uniform sampler2D u_atlas;
+layout(std140, set = 3, binding = 0) uniform UiUniforms {
+    float background_opacity;
+} u_ui;
 
 layout(location = 0) in vec2 v_uv;
 layout(location = 1) in vec3 v_fg;
@@ -29,11 +33,14 @@ float cellNoise(uint serial, uint col, uint row) {
 void main() {
     float a = texture(u_atlas, v_uv).r;
     bool oldLayer = (v_effect.x & 0x80000000u) != 0u;
-    // 0 where the cell's background IS the ground and the ground is nothing.
-    // src/gui/gui.zig sets that bit; the two flags above it are why the effect
-    // id is masked with 0x3fffffff here and in ui.vert.glsl.
-    float bgA = (v_effect.x & 0x40000000u) != 0u ? 0.0 : 1.0;
-    uint effect = v_effect.x & 0x3fffffffu;
+    // A block cursor is foreground chrome even though its fill occupies the
+    // cell background: keep it visible at WindowOpacity 0. Otherwise a clear
+    // theme ground has no coverage and ordinary backgrounds use the setting.
+    // The three high flags are shared with ui.vert.glsl and src/gui/gui.zig.
+    float bgA = (v_effect.x & 0x20000000u) != 0u ? 1.0
+        : (v_effect.x & 0x40000000u) != 0u ? 0.0
+        : clamp(u_ui.background_opacity, 0.0, 1.0);
+    uint effect = v_effect.x & 0x1fffffffu;
     float progress = clamp(uintBitsToFloat(v_effect.y), 0.0, 1.0);
     uint cellCol = v_effect.w & 0xffffu;
     uint cellRow = v_effect.w >> 16;
diff --git a/shaders/prebuilt/ui.frag.spv b/shaders/prebuilt/ui.frag.spv
index 4eb9993e..120438e7 100644
--- a/shaders/prebuilt/ui.frag.spv
+++ b/shaders/prebuilt/ui.frag.spv
diff --git a/shaders/prebuilt/ui.vert.glsl b/shaders/prebuilt/ui.vert.glsl
index 5ec596fe..d23b609c 100644
--- a/shaders/prebuilt/ui.vert.glsl
+++ b/shaders/prebuilt/ui.vert.glsl
@@ -14,9 +14,10 @@ layout(location = 3) in vec3 a_bg;
 layout(location = 4) in vec4 a_panel_rect;
 layout(location = 5) in vec4 a_present_rect;
 // effect id, eased-progress float bits, pane serial, local row/column packed
-// into one uint. The TWO high effect bits are flags — the frozen-old cell
-// layer and a see-through cell background — so the id is what is left below
-// them; integer transport preserves the exact cross-backend hash.
+// into one uint. The THREE high effect bits are flags — the frozen-old cell
+// layer, a see-through cell background and an opaque block-cursor fill — so
+// the id is what is left below them; integer transport preserves the exact
+// cross-backend hash.
 layout(location = 6) in uvec4 a_effect;
 
 layout(location = 0) out vec2 v_uv;
@@ -55,7 +56,7 @@ void main() {
         v_cell_uv = vec2(0.0, 1.0);
     }
 
-    uint effect = a_effect.x & 0x3fffffffu;
+    uint effect = a_effect.x & 0x1fffffffu;
     if (effect == 1u || effect == 2u || effect == 5u) {
         // NDC y points up, so a top-left/bottom-right box has a NEGATIVE y
         // delta. Preserve that sign or every local y is mirrored/outside.
diff --git a/shaders/prebuilt/ui.vert.spv b/shaders/prebuilt/ui.vert.spv
index 08e81e42..659049dd 100644
--- a/shaders/prebuilt/ui.vert.spv
+++ b/shaders/prebuilt/ui.vert.spv
diff --git a/shaders/ui.frag.glsl b/shaders/ui.frag.glsl
index 69cb63b9..3c366602 100644
--- a/shaders/ui.frag.glsl
+++ b/shaders/ui.frag.glsl
@@ -1,12 +1,16 @@
 #version 450
 
 // Sample the glyph atlas (R = coverage 0..1) and mix the cell's bg up to its fg
-// by that coverage. Output is PREMULTIPLIED: an opaque cell is unchanged, and a
-// cell whose background is the see-through ground (config.gui_transparent, a
-// theme with no bg of its own) contributes only its ink, at the ink's own
-// coverage, so the compositor keeps the rest.
+// by that coverage. Output is PREMULTIPLIED: an opaque cell is unchanged.
+// WindowOpacity changes only the ground's coverage, never the glyph's ink.
+// A cell whose background is the see-through ground (config.gui_transparent,
+// a theme with no bg of its own) still contributes only its ink, at the ink's
+// own coverage, so the compositor keeps the rest.
 
 layout(set = 2, binding = 0) uniform sampler2D u_atlas;
+layout(std140, set = 3, binding = 0) uniform UiUniforms {
+    float background_opacity;
+} u_ui;
 
 layout(location = 0) in vec2 v_uv;
 layout(location = 1) in vec3 v_fg;
@@ -29,11 +33,14 @@ float cellNoise(uint serial, uint col, uint row) {
 void main() {
     float a = texture(u_atlas, v_uv).r;
     bool oldLayer = (v_effect.x & 0x80000000u) != 0u;
-    // 0 where the cell's background IS the ground and the ground is nothing.
-    // src/gui/gui.zig sets that bit; the two flags above it are why the effect
-    // id is masked with 0x3fffffff here and in ui.vert.glsl.
-    float bgA = (v_effect.x & 0x40000000u) != 0u ? 0.0 : 1.0;
-    uint effect = v_effect.x & 0x3fffffffu;
+    // A block cursor is foreground chrome even though its fill occupies the
+    // cell background: keep it visible at WindowOpacity 0. Otherwise a clear
+    // theme ground has no coverage and ordinary backgrounds use the setting.
+    // The three high flags are shared with ui.vert.glsl and src/gui/gui.zig.
+    float bgA = (v_effect.x & 0x20000000u) != 0u ? 1.0
+        : (v_effect.x & 0x40000000u) != 0u ? 0.0
+        : clamp(u_ui.background_opacity, 0.0, 1.0);
+    uint effect = v_effect.x & 0x1fffffffu;
     float progress = clamp(uintBitsToFloat(v_effect.y), 0.0, 1.0);
     uint cellCol = v_effect.w & 0xffffu;
     uint cellRow = v_effect.w >> 16;
diff --git a/shaders/ui.vert.glsl b/shaders/ui.vert.glsl
index 5ec596fe..d23b609c 100644
--- a/shaders/ui.vert.glsl
+++ b/shaders/ui.vert.glsl
@@ -14,9 +14,10 @@ layout(location = 3) in vec3 a_bg;
 layout(location = 4) in vec4 a_panel_rect;
 layout(location = 5) in vec4 a_present_rect;
 // effect id, eased-progress float bits, pane serial, local row/column packed
-// into one uint. The TWO high effect bits are flags — the frozen-old cell
-// layer and a see-through cell background — so the id is what is left below
-// them; integer transport preserves the exact cross-backend hash.
+// into one uint. The THREE high effect bits are flags — the frozen-old cell
+// layer, a see-through cell background and an opaque block-cursor fill — so
+// the id is what is left below them; integer transport preserves the exact
+// cross-backend hash.
 layout(location = 6) in uvec4 a_effect;
 
 layout(location = 0) out vec2 v_uv;
@@ -55,7 +56,7 @@ void main() {
         v_cell_uv = vec2(0.0, 1.0);
     }
 
-    uint effect = a_effect.x & 0x3fffffffu;
+    uint effect = a_effect.x & 0x1fffffffu;
     if (effect == 1u || effect == 2u || effect == 5u) {
         // NDC y points up, so a top-left/bottom-right box has a NEGATIVE y
         // delta. Preserve that sign or every local y is mirrored/outside.