From bc51c3834928e388d16cc4b286da0574e3d94c32 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Sun, 1 Jul 2018 22:02:06 +0200
Subject: interactor: move animation

---
 interactor/game.js | 93 ++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 83 insertions(+), 10 deletions(-)

diff --git a/interactor/game.js b/interactor/game.js
index a9ecf2e..15ab83b 100644
--- a/interactor/game.js
+++ b/interactor/game.js
@@ -47,6 +47,14 @@ function cellY(i) {return (cellSize + 1) * ~~(i / N);}
 function cellMidX(i) {return (cellSize + 1) * (i % N + 0.5);}
 function cellMidY(i) {return (cellSize + 1) * (~~(i / N) + 0.5);}
 
+var tileDrawers = [
+	function(px, py) {},
+	function(px, py) { drawCircle(px, py, "#ffffff"); },
+	function(px, py) { drawKing(px, py); },
+	function(px, py) {},  // unused
+	function(px, py) { drawCircle(px, py, "#000000"); },
+];
+
 function redraw() {
 	ctx.fillStyle = "#e0c29f";
 	ctx.fillRect(0, 0, cvsSize, cvsSize);
@@ -65,16 +73,8 @@ function redraw() {
 	}
 	ctx.stroke();
 
-	var drawers = [
-		function() {},
-		function(px, py) { drawCircle(px, py, "#ffffff"); },
-		function(px, py) { drawKing(px, py); },
-		function() {},
-		function(px, py) { drawCircle(px, py, "#000000"); },
-	];
-
 	for (var i = 0; i < N * N; i++) {
-		drawers[board[i]](cellMidX(i), cellMidY(i));
+		tileDrawers[board[i]](cellMidX(i), cellMidY(i));
 	}
 
 	if (lastMove != null) {
@@ -92,6 +92,76 @@ function redraw() {
 	}
 }
 
+var animateSlideDuration = 0.2;
+function animateSlideInterpolate(a, b, t) {return (1-t) * a + t * b;}
+
+var animateSlideState = {
+	value: null,
+	move: null,
+	progress: null,
+	lastStamp: null,
+	imgdata: null,
+	aniframe: null,
+};
+
+function animateSlide(mv) {
+	cancelAnimateSlide();
+
+	var value = board[mv.from];
+
+	// Bit of a hack, the board being global state. We capture the imgdata while it's
+	// hot, to be able to repeatedly re-apply it during the animation.
+	board[mv.from] = EMPTY;
+	redraw();
+	animateSlideState.imgdata = ctx.getImageData(0, 0, cvsSize, cvsSize);
+	board[mv.from] = value;
+
+	animateSlideState.value = value;
+	animateSlideState.move = mv;
+	animateSlideState.progress = 0;
+	animateSlideState.lastStamp = performance.now();
+	animateSlideState.aniframe = requestAnimationFrame(animateFrame);
+
+	animateFrame(animateSlideState.lastStamp);
+}
+
+function animateFrame(stamp) {
+	// stamp can be 0 in case of the first frame
+
+	var st = animateSlideState;
+
+	var delta = stamp - st.lastStamp;
+	st.lastStamp = stamp;
+	st.progress += delta / 1000;
+
+	if (st.progress >= animateSlideDuration) {
+		cancelAnimateSlide();
+		return;
+	}
+
+	ctx.putImageData(st.imgdata, 0, 0);
+
+	var x1 = cellMidX(st.move.from), y1 = cellMidY(st.move.from);
+	var x2 = cellMidX(st.move.to), y2 = cellMidY(st.move.to);
+	var x = animateSlideInterpolate(x1, x2, st.progress / animateSlideDuration);
+	var y = animateSlideInterpolate(y1, y2, st.progress / animateSlideDuration);
+	tileDrawers[st.value](x, y);
+
+	requestAnimationFrame(animateFrame);
+}
+
+function cancelAnimateSlide() {
+	if (animateSlideState.move == null) return;
+
+	board[animateSlideState.move.from] = EMPTY;
+	board[animateSlideState.move.to] = animateSlideState.value;
+	cancelAnimationFrame(animateSlideState.aniframe);
+
+	animateSlideState.move = null;
+
+	redraw();
+}
+
 function drawCircle(x, y, clr) {
 	ctx.fillStyle = clr;
 	ctx.beginPath();
@@ -214,11 +284,14 @@ function humanMove(mv) {
 }
 
 function processMove(mv) {
+	cancelAnimateSlide();
+
+	animateSlide(mv);
+
 	var captures = applyMove(mv);
 	addMoveLog(onturn, mv, captures);
 	onturn = -onturn;
 	lastMove = mv;
-	redraw();
 
 	var win = checkWin();
 	var msg = win == 1 ? "White won." : win == -1 ? "Black won." : null;
-- 
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