animation: six character-motion panel transitions, composed in the core so backends agree

1 files changed, 317 insertions, 9 deletions

diff --git a/src/panel_animation.zig b/src/panel_animation.zig
index 0451213d..e0cb32d3 100644
--- a/src/panel_animation.zig
+++ b/src/panel_animation.zig
@@ -11,6 +11,9 @@ pub const ascii_max_movement_frames: u16 = 12;
 pub const Easing = enum(u8) {
     linear,
     smooth,
+    /// Quintic ease-in-out. It creeps at both ends and crosses the middle of
+    /// the distance fast, inside the same frame count a linear walk would use.
+    smoother,
     in_cubic,
     out_cubic,
     out_back,
@@ -26,13 +29,27 @@ pub const Transition = enum(u8) {
     dissolve = 3,
     ascii = 4,
     vertical = 5,
+    // Character effects the core composes into Surface cells (see
+    // `composedByCore`). A backend never evaluates them: it receives finished
+    // glyphs, so these ids reach a shader only as "draw this panel batch".
+    edges = 6,
+    fall = 7,
+    wave = 8,
+    curtain = 9,
+    scramble = 10,
+    typewriter = 11,
 
     pub fn easing(effect: Transition) Easing {
         return switch (effect) {
-            .off, .dissolve => .smooth,
-            .slide, .vertical => .out_cubic,
+            .off, .dissolve, .wave => .smooth,
+            .slide, .vertical, .edges => .out_cubic,
             .zoom => .out_back,
-            .ascii => .linear,
+            // Character walks and per-cell locks read best with a slow start,
+            // a fast middle, and a slow settle over their fixed frame count.
+            .ascii, .fall, .scramble => .smoother,
+            // A sweep and a typewriter are constant-rate by definition: easing
+            // their head would make the pass visibly hesitate mid-pane.
+            .curtain, .typewriter => .linear,
         };
     }
 
@@ -47,11 +64,25 @@ pub const Transition = enum(u8) {
             // destination; nearby bytes still move one value at a time.
             .ascii => ascii_max_movement_frames + 1,
             .vertical => 12,
+            .edges, .curtain, .scramble => 12,
+            // Travelling motion needs a couple more samples than a lock or a
+            // rigid slide before it stops reading as a jump.
+            .fall, .wave, .typewriter => 14,
+        };
+    }
+
+    /// Character effects whose glyphs the core writes into the published
+    /// Surface. Every backend rasterizes the same finished cells, which is why
+    /// none of them owns a byte walk, a stagger, or a noise threshold.
+    pub fn composedByCore(effect: Transition) bool {
+        return switch (effect) {
+            .ascii, .edges, .fall, .wave, .curtain, .scramble, .typewriter => true,
+            .off, .slide, .zoom, .dissolve, .vertical => false,
         };
     }
 
     pub fn needsPreviousGrid(effect: Transition) bool {
-        return effect == .dissolve or effect == .ascii or effect == .vertical;
+        return effect == .dissolve or effect == .vertical or effect.composedByCore();
     }
 
     pub fn lifecycleOnly(effect: Transition) bool {
@@ -124,11 +155,14 @@ pub const Track = extern struct {
     }
 
     /// Geometry actually painted by every backend. Content transitions reveal
-    /// cells in place; slide, zoom, and vertical transform the panel rectangle.
+    /// or move cells inside the final rectangle; slide, zoom, and vertical
+    /// transform the panel rectangle itself.
     pub fn visualBox(track: Track) Box {
         return switch (track.effect) {
             .slide, .zoom, .vertical => track.presented(),
-            .off, .dissolve, .ascii => track.to,
+            .off, .dissolve => track.to,
+            // Every character effect stays inside the pane's final rectangle.
+            .ascii, .edges, .fall, .wave, .curtain, .scramble, .typewriter => track.to,
         };
     }
 
@@ -140,8 +174,9 @@ pub const Track = extern struct {
     }
 };
 
-/// Preset starting geometry for a newly-visible panel. Dissolve and ASCII
-/// animate content in place; slide, zoom, and vertical animate its rectangle.
+/// Preset starting geometry for a newly-visible panel. Dissolve and the
+/// character effects animate content in place; slide, zoom, and vertical
+/// animate its rectangle.
 pub fn openingBox(effect: Transition, target: Box, screen_width: u16) Box {
     return switch (effect) {
         .slide => blk: {
@@ -167,7 +202,10 @@ pub fn openingBox(effect: Transition, target: Box, screen_width: u16) Box {
             from.y += target.h;
             break :blk from;
         },
-        .off, .dissolve, .ascii => target,
+        .off, .dissolve => target,
+        // Character effects own the glyphs inside a fixed rectangle, so their
+        // panel opens at exactly its final geometry.
+        .ascii, .edges, .fall, .wave, .curtain, .scramble, .typewriter => target,
     };
 }
 
@@ -191,6 +229,7 @@ pub fn sample(easing: Easing, raw: f32) f32 {
     return switch (easing) {
         .linear => t,
         .smooth => t * t * (3.0 - 2.0 * t),
+        .smoother => t * t * t * (t * (6.0 * t - 15.0) + 10.0),
         .in_cubic => t * t * t,
         .out_cubic => 1.0 - (1.0 - t) * (1.0 - t) * (1.0 - t),
         // Robert Penner's ease-out-back polynomial. It intentionally travels
@@ -250,6 +289,129 @@ pub fn dissolveRevealed(serial: u32, col: u16, row: u16, raw_progress: f32) bool
     return cellNoise(serial, col, row) < t;
 }
 
+/// The pane-local cell grid a core-composed character effect walks. Origin and
+/// size use the same floor/ceil convention as the GUI cell-coordinate upload,
+/// so the core's composition and any backend port index the same glyph.
+pub const CellArea = struct {
+    x0: u16 = 0,
+    y0: u16 = 0,
+    cols: u16 = 1,
+    rows: u16 = 1,
+
+    pub fn of(box: Box) CellArea {
+        return .{
+            .x0 = floorCell(box.x),
+            .y0 = floorCell(box.y),
+            .cols = ceilCell(box.w),
+            .rows = ceilCell(box.h),
+        };
+    }
+};
+
+fn floorCell(value: f32) u16 {
+    return @intFromFloat(std.math.clamp(@floor(value), 0.0, @as(f32, std.math.maxInt(u16))));
+}
+
+fn ceilCell(value: f32) u16 {
+    return @intFromFloat(std.math.clamp(@ceil(value), 1.0, @as(f32, std.math.maxInt(u16))));
+}
+
+/// What one pane cell shows this frame under a core-composed character
+/// effect. `at` offsets are in cells and relative to the destination cell, so
+/// an all-zero offset is exactly the canonical glyph and every effect ends on
+/// the untouched final frame.
+pub const CharSource = union(enum) {
+    /// Nothing has arrived here yet: keep the frozen old cell.
+    old,
+    at: Offset,
+    /// Paint this printable byte in the destination cell's own style, whatever
+    /// that cell holds — a caret marching over empty space is still a caret.
+    byte: u8,
+    /// Paint this printable byte only where there is a glyph to churn. Noise
+    /// over blank cells would fill a pane with junk instead of letting its
+    /// text resolve out of noise.
+    churn: u8,
+
+    pub const Offset = struct { cols: i32 = 0, rows: i32 = 0 };
+
+    pub const settled: CharSource = .{ .at = .{} };
+};
+
+/// One cell of one core-composed character effect. Offsets travel with the
+/// glyph rather than blending it: a cell either holds a real glyph from the
+/// new grid, the frozen old glyph, or a churning byte, never a mix. A source
+/// outside the pane is the caller's cue to keep the old cell.
+pub fn charSource(track: Track, col: u16, row: u16, area: CellArea) CharSource {
+    const t = track.amount();
+    if (t >= 1.0) return .settled;
+    const w: f32 = @floatFromInt(area.cols);
+    const h: f32 = @floatFromInt(area.rows);
+    const c: f32 = @floatFromInt(col);
+    const r: f32 = @floatFromInt(row);
+    const remaining = 1.0 - t;
+    return switch (track.effect) {
+        // Whole rows arrive from the left and right screen edges, alternating.
+        // Sliding rigid rows is what keeps the glyphs crisp: one row is one
+        // rigid translation, so no cell ever samples two source glyphs.
+        .edges => blk: {
+            const travel = cellsOf(remaining * (w + 1.0));
+            break :blk .{ .at = .{ .cols = if (row % 2 == 0) travel else -travel } };
+        },
+        // Columns rain down, each with its own stable head start, so the pane
+        // fills from the top and the last glyphs land at the bottom.
+        .fall => blk: {
+            const local = staggered(t, cellNoise(track.serial, col, 0) * 0.4);
+            if (local <= 0.0) break :blk .old;
+            break :blk .{ .at = .{ .rows = cellsOf((1.0 - local) * (h + 1.0)) } };
+        },
+        // A vertical ripple travels left to right and its amplitude decays, so
+        // the pane settles out of a wave instead of a fade.
+        .wave => .{ .at = .{
+            .rows = cellsOf(remaining * @min(4.0, h) * @sin(c * 0.55 - t * 9.0)),
+        } },
+        // A curtain of glyphs marches in from the right, column by column, left
+        // to right; each column still has a short slide of its own.
+        .curtain => blk: {
+            const lead = t * (w + 1.0) - c;
+            if (lead <= 0.0) break :blk .old;
+            break :blk .{ .at = .{ .cols = -cellsOf(@max(0.0, 3.0 - lead)) } };
+        },
+        // Every cell churns through printable ASCII and locks onto its final
+        // glyph at its own stable threshold: the pane resolves out of noise.
+        .scramble => blk: {
+            if (t >= cellNoise(track.serial, col, row) * 0.8) break :blk .settled;
+            const churn = cellNoise(
+                track.serial ^ (@as(u32, track.frame) *% 0x27d4_eb2f),
+                col,
+                row,
+            );
+            break :blk .{ .churn = @intCast(33 + @min(93, @as(u32, @intFromFloat(churn * 94.0)))) };
+        },
+        // Reading-order reveal with a caret sitting on the write head.
+        .typewriter => blk: {
+            const head = t * w * h;
+            const index = r * w + c;
+            if (index + 1.0 <= head) break :blk .settled;
+            if (index <= head) break :blk .{ .byte = '_' };
+            break :blk .old;
+        },
+        // PanelAscii walks its own byte distance per cell, and the geometry
+        // effects never reach this path at all.
+        .off, .slide, .zoom, .dissolve, .vertical, .ascii => .settled,
+    };
+}
+
+fn cellsOf(distance: f32) i32 {
+    return @intFromFloat(@round(std.math.clamp(distance, -65535.0, 65535.0)));
+}
+
+/// Remap track progress into one cell's own window. A stagger delays a glyph
+/// without making the effect as a whole end after its last frame.
+fn staggered(t: f32, delay: f32) f32 {
+    if (delay >= 1.0) return t;
+    return (t - delay) / (1.0 - delay);
+}
+
 test "easing presets have exact endpoints and intended shapes" {
     inline for (std.enums.values(Easing)) |easing| {
         try std.testing.expectEqual(@as(f32, 0), sample(easing, 0));
@@ -259,6 +421,13 @@ test "easing presets have exact endpoints and intended shapes" {
     try std.testing.expect(sample(.in_cubic, 0.5) < sample(.linear, 0.5));
     try std.testing.expect(sample(.out_cubic, 0.5) > sample(.linear, 0.5));
     try std.testing.expect(sample(.out_back, 0.8) > 1.0);
+    // Slow at both ends, fast through the middle, and symmetric about the
+    // halfway point: the same curve the integer byte walk reproduces.
+    try std.testing.expectEqual(@as(f32, 0.5), sample(.smoother, 0.5));
+    try std.testing.expect(sample(.smoother, 0.15) < sample(.smooth, 0.15));
+    try std.testing.expect(sample(.smoother, 0.85) > sample(.smooth, 0.85));
+    try std.testing.expect(sample(.smoother, 0.6) - sample(.smoother, 0.4) >
+        sample(.linear, 0.6) - sample(.linear, 0.4));
 }
 
 test "transition progress completes exactly" {
@@ -278,6 +447,145 @@ test "transition progress completes exactly" {
     try std.testing.expect(opening.h > 40);
 }
 
+test "character effects are core-composed and settle on the canonical glyph" {
+    const box: Box = .{ .x = 4, .y = 2, .w = 20, .h = 6 };
+    const area: CellArea = .of(box);
+    try std.testing.expectEqual(@as(u16, 4), area.x0);
+    try std.testing.expectEqual(@as(u16, 2), area.y0);
+    try std.testing.expectEqual(@as(u16, 20), area.cols);
+    try std.testing.expectEqual(@as(u16, 6), area.rows);
+
+    inline for (std.enums.values(Transition)) |effect| {
+        if (comptime !effect.composedByCore()) continue;
+        // Core composition needs the frozen old grid for every glyph which has
+        // not arrived, so no character effect may animate without it.
+        try std.testing.expect(effect.needsPreviousGrid());
+        if (comptime effect == .ascii) continue; // owns its own per-cell byte walk
+
+        const last: Track = .{ .effect = effect, .frame = effect.frames() - 1, .to = box };
+        const first: Track = .{ .effect = effect, .frame = 0, .to = box };
+        var moving = false;
+        var row: u16 = 0;
+        while (row < area.rows) : (row += 1) {
+            var col: u16 = 0;
+            while (col < area.cols) : (col += 1) {
+                // The last active sample is the exact canonical grid: no cell
+                // is displaced, churning, or still frozen.
+                try std.testing.expectEqual(CharSource.settled, charSource(last, col, row, area));
+                if (!std.meta.eql(CharSource.settled, charSource(first, col, row, area)))
+                    moving = true;
+            }
+        }
+        try std.testing.expect(moving);
+    }
+}
+
+test "each character effect moves glyphs along its own axis" {
+    const box: Box = .{ .w = 30, .h = 8 };
+    const area: CellArea = .of(box);
+
+    // Rows alternate which screen edge they come from, and every glyph in a row
+    // travels as one rigid slide: one offset, no vertical component.
+    var edges: Track = .{ .effect = .edges, .frame = 2, .to = box };
+    const even = charSource(edges, 5, 0, area).at;
+    const odd = charSource(edges, 5, 1, area).at;
+    try std.testing.expect(even.cols > 0);
+    try std.testing.expectEqual(-even.cols, odd.cols);
+    try std.testing.expectEqual(@as(i32, 0), even.rows);
+    try std.testing.expectEqual(even, charSource(edges, 17, 0, area).at);
+    edges.frame = 5;
+    try std.testing.expect(charSource(edges, 5, 0, area).at.cols < even.cols);
+
+    // Falling columns are vertical only, staggered, and sample from below the
+    // destination because the new text is still above the pane.
+    const fall: Track = .{ .effect = .fall, .frame = 4, .to = box };
+    var falling = false;
+    var col: u16 = 0;
+    while (col < area.cols) : (col += 1) switch (charSource(fall, col, 0, area)) {
+        .old => {},
+        .byte, .churn => return error.FallShouldNotChurn,
+        .at => |offset| {
+            try std.testing.expectEqual(@as(i32, 0), offset.cols);
+            try std.testing.expect(offset.rows >= 0);
+            if (offset.rows > 0) falling = true;
+        },
+    };
+    try std.testing.expect(falling);
+
+    // The wave displaces rows both ways as it travels, and only rows.
+    const wave: Track = .{ .effect = .wave, .frame = 1, .to = box };
+    var above = false;
+    var below = false;
+    col = 0;
+    while (col < area.cols) : (col += 1) {
+        const offset = charSource(wave, col, 3, area).at;
+        try std.testing.expectEqual(@as(i32, 0), offset.cols);
+        if (offset.rows < 0) above = true;
+        if (offset.rows > 0) below = true;
+    }
+    try std.testing.expect(above and below);
+
+    // The curtain has a head: columns behind it hold the old grid, columns the
+    // head has passed are settled, and the head itself is still sliding.
+    const curtain: Track = .{ .effect = .curtain, .frame = 5, .to = box };
+    try std.testing.expectEqual(CharSource.settled, charSource(curtain, 0, 0, area));
+    try std.testing.expectEqual(CharSource{ .old = {} }, charSource(curtain, 29, 0, area));
+    var sliding = false;
+    col = 0;
+    while (col < area.cols) : (col += 1) switch (charSource(curtain, col, 0, area)) {
+        .at => |offset| if (offset.cols < 0) {
+            sliding = true;
+        },
+        .old, .byte, .churn => {},
+    };
+    try std.testing.expect(sliding);
+
+    // Scramble churns printable ASCII per cell and per frame, then locks. It
+    // asks for churn rather than an unconditional byte, so the compositor can
+    // keep the pane's blank space blank.
+    var scramble: Track = .{ .effect = .scramble, .frame = 3, .to = box };
+    var churning: usize = 0;
+    var locked: usize = 0;
+    var changed = false;
+    col = 0;
+    while (col < area.cols) : (col += 1) switch (charSource(scramble, col, 0, area)) {
+        .churn => |byte| {
+            try std.testing.expect(byte >= ' ' and byte <= '~');
+            churning += 1;
+            scramble.frame = 4;
+            switch (charSource(scramble, col, 0, area)) {
+                .churn => |next| changed = changed or next != byte,
+                .old, .at, .byte => {},
+            }
+            scramble.frame = 3;
+        },
+        .at => locked += 1,
+        .old, .byte => return error.ScrambleShouldNotFreeze,
+    };
+    try std.testing.expect(churning > 0 and locked > 0 and changed);
+
+    // The typewriter writes in reading order with a caret on its head.
+    const typewriter: Track = .{ .effect = .typewriter, .frame = 7, .to = box };
+    try std.testing.expectEqual(CharSource.settled, charSource(typewriter, 0, 0, area));
+    try std.testing.expectEqual(
+        CharSource{ .old = {} },
+        charSource(typewriter, area.cols - 1, area.rows - 1, area),
+    );
+    var carets: usize = 0;
+    var row: u16 = 0;
+    while (row < area.rows) : (row += 1) {
+        col = 0;
+        while (col < area.cols) : (col += 1) switch (charSource(typewriter, col, row, area)) {
+            .byte => |byte| {
+                try std.testing.expectEqual(@as(u8, '_'), byte);
+                carets += 1;
+            },
+            .old, .at, .churn => {},
+        };
+    }
+    try std.testing.expectEqual(@as(usize, 1), carets);
+}
+
 test "opening presets separate geometry and content transitions" {
     const target: Box = .{ .x = 30, .y = 2, .w = 20, .h = 8 };
     try std.testing.expectEqual(target, openingBox(.ascii, target, 80));