1 files changed, 227 insertions, 0 deletions
diff --git a/dot_config/ghostty/shaders/crisp_cursor_tail.glsl b/dot_config/ghostty/shaders/crisp_cursor_tail.glsl
new file mode 100644
index 0000000..a99a3ba
--- /dev/null
+++ b/dot_config/ghostty/shaders/crisp_cursor_tail.glsl
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+// crisp_cursor_tail_v3.glsl
+//
+// A deliberately crisp Ghostty cursor trail:
+// - no blur
+// - no bloom or additive blending
+// - the real cursor is never enlarged
+// - several same-size cursor silhouettes fade behind it
+//
+// Requires Ghostty 1.3.0 or newer.
+
+const float DURATION = 0.200;
+
+// Strong enough to be clearly visible without additive glow.
+const float MAX_OPACITY = 0.80;
+
+const int TRAIL_COPIES = 13;
+
+// Maximum trail length in approximate cursor-cell lengths.
+const float MAX_TRAIL_CELLS = 3.5;
+
+// Ignore tiny sub-cell position changes.
+const float MIN_MOVE_CELLS = 0.20;
+
+// Ghostty cannot tell the shader whether a move came from typing or navigation.
+// Suppressing one-cell horizontal advances is the dependable approximation.
+const bool SUPPRESS_SINGLE_CELL_HORIZONTAL = true;
+const float CELL_TOLERANCE = 0.20;
+
+// Suppress the large last-column -> first-column jump produced by line wrap.
+const float WRAP_MIN_HORIZONTAL_CELLS = 4.0;
+
+// Do not animate stale previous/current cursor state immediately after focus is
+// restored. This also covers delayed frames from an unfocused surface.
+const float REFOCUS_GUARD_TIME = 0.060;
+
+// Higher values make the far end fade more strongly.
+const float SPATIAL_FADE_POWER = 0.65;
+
+// false: animate horizontal, vertical, and diagonal movement.
+// true: only animate left/right movement.
+const bool HORIZONTAL_ONLY = false;
+
+vec3 srgbToLinear(vec3 c) {
+    return mix(
+        c / 12.92,
+        pow((c + 0.055) / 1.055, vec3(2.4)),
+        step(vec3(0.04045), c)
+    );
+}
+
+// Convert pixel coordinates to the normalized coordinate system used by the
+// known-working Ghostty cursor shaders. Positions use isPosition=1.0;
+// dimensions use isPosition=0.0.
+vec2 toNormalized(vec2 value, float isPosition) {
+    return (value * 2.0 - iResolution.xy * isPosition) / iResolution.y;
+}
+
+float rectangleSdf(vec2 point, vec2 center, vec2 halfSize) {
+    vec2 d = abs(point - center) - halfSize;
+    return length(max(d, 0.0)) + min(max(d.x, d.y), 0.0);
+}
+
+float rectangleMask(vec2 point, vec2 center, vec2 halfSize) {
+    // Hard edge: intentionally no antialiasing or blur.
+    return step(rectangleSdf(point, center, halfSize), 0.0);
+}
+
+float easeOutCubic(float x) {
+    float y = 1.0 - x;
+    return 1.0 - y * y * y;
+}
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+#if !defined(WEB)
+    fragColor = texture(iChannel0, fragCoord.xy / iResolution.xy);
+#endif
+
+    // Ghostty deliberately renders unfocused surfaces less frequently. Drawing
+    // from their stale cursor uniforms causes detached or hollow-looking trails.
+    if (iFocus <= 0 || (iTime - iTimeFocus) < REFOCUS_GUARD_TIME) {
+        return;
+    }
+
+    if (iResolution.x <= 0.0 || iResolution.y <= 0.0 ||
+        any(lessThanEqual(iCurrentCursor.zw, vec2(0.0))) ||
+        any(lessThanEqual(iPreviousCursor.zw, vec2(0.0)))) {
+        return;
+    }
+
+    vec2 point = toNormalized(fragCoord, 1.0);
+
+    vec4 currentCursor = vec4(
+        toNormalized(iCurrentCursor.xy, 1.0),
+        toNormalized(iCurrentCursor.zw, 0.0)
+    );
+
+    vec4 previousCursor = vec4(
+        toNormalized(iPreviousCursor.xy, 1.0),
+        toNormalized(iPreviousCursor.zw, 0.0)
+    );
+
+    // Ghostty cursor.xy is the left/top corner.
+    vec2 offsetFactor = vec2(-0.5, 0.5);
+    vec2 currentCenter =
+        currentCursor.xy - currentCursor.zw * offsetFactor;
+    vec2 previousCenter =
+        previousCursor.xy - previousCursor.zw * offsetFactor;
+
+    vec2 movement = previousCenter - currentCenter;
+    float movementLength = length(movement);
+
+    if (movementLength <= 0.000001) {
+        return;
+    }
+
+    if (HORIZONTAL_ONLY && abs(movement.y) > 0.00001) {
+        return;
+    }
+
+    vec2 direction = movement / movementLength;
+
+    // Approximate one cell along the direction of travel.
+    float cellLength =
+        abs(direction.x) * currentCursor.z +
+        abs(direction.y) * currentCursor.w;
+    cellLength = max(cellLength, 0.000001);
+
+    if ((movementLength / cellLength) < MIN_MOVE_CELLS) {
+        return;
+    }
+
+    float horizontalCells = abs(movement.x) / currentCursor.z;
+    float verticalCells = abs(movement.y) / currentCursor.w;
+
+    bool singleCellHorizontal =
+        verticalCells < CELL_TOLERANCE &&
+        abs(horizontalCells - 1.0) <= CELL_TOLERANCE;
+    if (SUPPRESS_SINGLE_CELL_HORIZONTAL && singleCellHorizontal) {
+        return;
+    }
+
+    bool likelyLineWrap =
+        abs(verticalCells - 1.0) <= CELL_TOLERANCE &&
+        horizontalCells >= WRAP_MIN_HORIZONTAL_CELLS;
+    if (likelyLineWrap) {
+        return;
+    }
+
+    float elapsed = iTime - iTimeCursorChange;
+    if (elapsed < 0.0) {
+        return;
+    }
+    float progress = clamp(elapsed / DURATION, 0.0, 1.0);
+
+    if (progress >= 1.0) {
+        return;
+    }
+
+    // Linear persistence keeps the trail clearly visible for most of its
+    // lifetime. The previous cubic curve became almost invisible too quickly.
+    float remaining = 1.0 - progress;
+
+    // Keep opacity strong through the first half, then fade smoothly.
+    float timeOpacity = pow(remaining, 0.85);
+
+    float cappedLength =
+        min(movementLength, MAX_TRAIL_CELLS * cellLength);
+
+    vec2 cappedPreviousCenter =
+        currentCenter + direction * cappedLength;
+
+    float trailAlpha = 0.0;
+
+    for (int index = 1; index <= TRAIL_COPIES; ++index) {
+        float distanceRank =
+            float(index) / float(TRAIL_COPIES);
+
+        // At t=0, copies span current -> previous. As time advances they all
+        // collapse toward current, leaving the real cursor unchanged.
+        vec2 copyCenter = mix(
+            currentCenter,
+            cappedPreviousCenter,
+            distanceRank * remaining
+        );
+
+        float copyMask = rectangleMask(
+            point,
+            copyCenter,
+            currentCursor.zw * 0.5
+        );
+
+        // Nearest copies are strongest; distant copies are progressively faint.
+        float spatialFade = pow(
+            1.0 - distanceRank * 0.82,
+            SPATIAL_FADE_POWER
+        );
+
+        float copyAlpha =
+            MAX_OPACITY * spatialFade * timeOpacity;
+
+        // max(), not addition: overlapping copies never become a bright glow.
+        trailAlpha = max(
+            trailAlpha,
+            copyMask * copyAlpha
+        );
+    }
+
+    // Cut out the actual cursor rectangle so its apparent size and contrast are
+    // controlled entirely by Ghostty, not by this shader.
+    float currentCursorMask = rectangleMask(
+        point,
+        currentCenter,
+        currentCursor.zw * 0.5
+    );
+    trailAlpha *= 1.0 - currentCursorMask;
+
+    vec4 trailColor = vec4(
+        srgbToLinear(iCurrentCursorColor.rgb),
+        iCurrentCursorColor.a
+    );
+
+    fragColor = mix(
+        fragColor,
+        trailColor,
+        trailAlpha * trailColor.a
+    );
+}