A tab change reveal animation

kitty/shaders.c

@@ -2359,6 +2359,7 @@ run_custom_end_shader(OSWindow *os_window, float sx, float sy, monotonic_t now)
         float mouse_pos[4];
         float mouse_button_pressed[4];
         float active_window_geometry[4];
+        float central_area[4];
         float cursor_trail_corners_x[4];
         float cursor_trail_corners_y[4];
         float cursor_trail_edge[4];
@@ -2474,6 +2475,17 @@ run_custom_end_shader(OSWindow *os_window, float sx, float sy, monotonic_t now)
         d->active_window_geometry[2] = (float)(active_win_geom.right - active_win_geom.left) / vpw;
         d->active_window_geometry[3] = (float)(active_win_geom.bottom - active_win_geom.top) / vph;
     }
+    if (vpw > 0 && vph > 0) {
+        Region central_rgn = {0}, tab_bar_rgn = {0};
+        os_window_regions(os_window, &central_rgn, &tab_bar_rgn);
+        d->central_area[0] = (float)central_rgn.left / vpw;
+        d->central_area[1] = 1.f - (float)central_rgn.bottom / vph;
+        d->central_area[2] = (float)(central_rgn.right - central_rgn.left) / vpw;
+        d->central_area[3] = (float)(central_rgn.bottom - central_rgn.top) / vph;
+    } else {
+        d->central_area[2] = 1.f;
+        d->central_area[3] = 1.f;
+    }
     unmap_vao_buffer(custom_end_vao_idx, 0);
     bind_vao_uniform_buffer(custom_end_vao_idx, 0, CUSTOM_END_DATA_BINDING_POINT);
 

kitty/shaders/custom/tab-focus.pipeline

@@ -0,0 +1,7 @@
+startgroup
+    animation_start tab-change
+    animation_stop 600
+    animation_curve ease-out
+    animation_step 16
+    shaders tab-focus
+endgroup

kitty/shaders/custom/tab-focus.slang

@@ -0,0 +1,96 @@
+#language slang 2026
+// Copyright (C) 2026 Kovid Goyal <kovid at kovidgoyal.net>
+// Distributed under terms of the GPLv3 license.
+//
+// Tab-change reveal shader
+// Plays a brief reveal animation whenever the active tab changes.
+// The reveal direction for wipe-based modes is derived from d.central_area:
+// the wipe starts at whichever edge of the content area is furthest from the
+// viewport boundary — that edge is where the tab bar sits.
+//
+// ANIMATION_TYPE selects the effect:
+//   0 = FADE   — uniform brightness fade-in over the whole screen
+//   1 = WIPE   — a single swept edge travelling away from the tab bar
+//   2 = BLINDS — sequential strip reveals sweeping away from the tab bar
+//   3 = IRIS   — circular iris expanding from the centre of the content area
+
+import kitty_custom_shader_types;
+
+// 0=FADE, 1=WIPE, 2=BLINDS, 3=IRIS
+extern static const int ANIMATION_TYPE = 1;
+
+// Number of strips for ANIMATION_TYPE == 2 (BLINDS).
+extern static const int NUM_BLINDS = 8;
+
+// Soft-edge width in UV units used by WIPE and IRIS.
+extern static const float EDGE_SOFTNESS = 0.04;
+
+// Returns a value in [0, 1] for this pixel: 0 at the tab-bar edge of the
+// content area, 1 at the opposite edge.  The wipe sweeps from 0 toward 1.
+float wipe_pixel_pos(float2 uv, float4 ca) {
+    float gap_left   = ca.x;
+    float gap_right  = 1.0 - (ca.x + ca.z);
+    float gap_bottom = ca.y;
+    float gap_top    = 1.0 - (ca.y + ca.w);
+    float max_gap    = max(max(gap_left, gap_right), max(gap_bottom, gap_top));
+
+    float pos;
+    if (max_gap == gap_top) {
+        // Tab bar at top — sweep from top-of-content downward
+        pos = (ca.y + ca.w - uv.y) / ca.w;
+    } else if (max_gap == gap_bottom) {
+        // Tab bar at bottom — sweep from bottom-of-content upward
+        pos = (uv.y - ca.y) / ca.w;
+    } else if (max_gap == gap_left) {
+        // Tab bar at left — sweep from left-of-content rightward
+        pos = (uv.x - ca.x) / ca.z;
+    } else {
+        // Tab bar at right — sweep from right-of-content leftward
+        pos = (ca.x + ca.z - uv.x) / ca.z;
+    }
+    return clamp(pos, 0.0, 1.0);
+}
+
+public float4 fragment_main(
+    float4 color,
+    KittyTextures t,
+    KittyCustomShaderData d,
+    float4 viewport,
+    float animation_progress
+) {
+    float4 ca = d.central_area;
+    if (ca.z <= 0.0 || ca.w <= 0.0) return color;
+
+    float p = animation_progress;
+    float brightness;
+
+    if (ANIMATION_TYPE == 0) {
+        // FADE: uniform ramp over the whole frame
+        brightness = p;
+    } else if (ANIMATION_TYPE == 1) {
+        // WIPE: single swept edge with soft falloff
+        float pixel_pos = wipe_pixel_pos(t.pos, ca);
+        // 1.0 where revealed (pixel_pos < p), 0.0 where not yet reached
+        brightness = 1.0 - smoothstep(p - EDGE_SOFTNESS, p + EDGE_SOFTNESS, pixel_pos);
+    } else if (ANIMATION_TYPE == 2) {
+        // BLINDS: strips opening in sequence from the tab-bar side
+        float pixel_pos = wipe_pixel_pos(t.pos, ca);
+        float inv_n     = 1.0 / float(NUM_BLINDS);
+        float strip_idx = floor(pixel_pos * float(NUM_BLINDS));
+        float strip_start = strip_idx * inv_n;
+        // Progress local to this strip: 0 when it starts opening, 1 when fully open
+        float strip_p   = clamp((p - strip_start) / inv_n, 0.0, 1.0);
+        // Position within the strip (0 at tab-bar side, 1 at far side)
+        float local     = fract(pixel_pos * float(NUM_BLINDS));
+        float soft      = 0.1;
+        brightness = 1.0 - smoothstep(strip_p - soft, strip_p + soft, local);
+    } else {
+        // IRIS: circular reveal expanding from the centre of the content area
+        float2 ca_center = ca.xy + ca.zw * 0.5;
+        float half_diag  = length(ca.zw * 0.5);
+        float dist       = length(t.pos - ca_center) / max(half_diag, 0.001);
+        brightness = 1.0 - smoothstep(p - EDGE_SOFTNESS, p + EDGE_SOFTNESS, dist);
+    }
+
+    return float4(color.rgb * brightness, color.a);
+}

kitty/shaders/custom/types.slang

@@ -22,6 +22,11 @@ public struct KittyCustomShaderData {
     // .xy = lower-left corner of the window, .zw = width and height.
     // All components are zero when no active window was rendered this frame.
     public float4 active_window_geometry;
+    // Geometry of the central content area of the OS window (the tab area, excluding any tab bar)
+    // in UV co-ordinates (origin bottom-left).
+    // .xy = lower-left corner, .zw = width and height.
+    // Equals the full viewport when no tab bar is visible.
+    public float4 central_area;
 
     // Cursor trail state (UV coordinates, origin bottom-left, (1,1) top-right).
     // All fields are zero when the cursor_trail kitty option is disabled or the trail is inactive.