+
+/**
+ * Proxy for CanvasRenderingContext2D which drops moveTo/lineTo calls which are
+ * superfluous. It accumulates all movements which haven't changed the x-value
+ * and only applies the two with the most extreme y-values.
+ *
+ * Calls to lineTo/moveTo must have non-decreasing x-values.
+ */
+DygraphCanvasRenderer._fastCanvasProxy = function(context) {
+ var pendingActions = []; // array of [type, x, y] tuples
+ var lastRoundedX = null;
+ var extremeYs = null; // [minY, maxY] for lastRoundedX
+
+ var LINE_TO = 1,
+ MOVE_TO = 2;
+
+ var actionCount = 0; // number of moveTos and lineTos passed to context.
+
+ // Drop superfluous motions
+ // Assumes all pendingActions have the same (rounded) x-value.
+ var compressActions = function(opt_losslessOnly) {
+ if (pendingActions.length <= 1) return;
+
+ // Lossless compression: drop inconsequential moveTos.
+ for (var i = pendingActions.length - 1; i > 0; i--) {
+ var action = pendingActions[i];
+ if (action[0] == MOVE_TO) {
+ var prevAction = pendingActions[i - 1];
+ if (prevAction[1] == action[1] && prevAction[2] == action[2]) {
+ pendingActions.splice(i, 1);
+ }
+ }
+ }
+
+ // Lossless compression: ... drop consecutive moveTos ...
+ for (var i = 0; i < pendingActions.length - 1; /* incremented internally */) {
+ var action = pendingActions[i];
+ if (action[0] == MOVE_TO && pendingActions[i + 1][0] == MOVE_TO) {
+ pendingActions.splice(i, 1);
+ } else {
+ i++;
+ }
+ }
+
+ // Lossy compression: ... drop all but the extreme y-values ...
+ if (pendingActions.length > 2 && !opt_losslessOnly) {
+ // keep an initial moveTo, but drop all others.
+ var startIdx = 0;
+ if (pendingActions[0][0] == MOVE_TO) startIdx++;
+ var minIdx = null, maxIdx = null;
+ for (var i = startIdx; i < pendingActions.length; i++) {
+ var action = pendingActions[i];
+ if (action[0] != LINE_TO) continue;
+ if (minIdx === null && maxIdx === null) {
+ minIdx = i;
+ maxIdx = i;
+ } else {
+ var y = action[2];
+ if (y < pendingActions[minIdx][2]) {
+ minIdx = i;
+ } else if (y > pendingActions[maxIdx][2]) {
+ maxIdx = i;
+ }
+ }
+ }
+ var minAction = pendingActions[minIdx],
+ maxAction = pendingActions[maxIdx];
+ pendingActions.splice(startIdx, pendingActions.length - startIdx);
+ if (minIdx < maxIdx) {
+ pendingActions.push(minAction);
+ pendingActions.push(maxAction);
+ } else if (minIdx > maxIdx) {
+ pendingActions.push(maxAction);
+ pendingActions.push(minAction);
+ } else {
+ pendingActions.push(minAction);
+ }
+ }
+ };
+
+ var flushActions = function(opt_noLossyCompression) {
+ compressActions(opt_noLossyCompression);
+ for (var i = 0, len = pendingActions.length; i < len; i++) {
+ var action = pendingActions[i];
+ if (action[0] == LINE_TO) {
+ context.lineTo(action[1], action[2]);
+ } else if (action[0] == MOVE_TO) {
+ context.moveTo(action[1], action[2]);
+ }
+ }
+ actionCount += pendingActions.length;
+ pendingActions = [];
+ };
+
+ var addAction = function(action, x, y) {
+ var rx = Math.round(x);
+ if (lastRoundedX === null || rx != lastRoundedX) {
+ flushActions();
+ lastRoundedX = rx;
+ }
+ pendingActions.push([action, x, y]);
+ };
+
+ return {
+ moveTo: function(x, y) {
+ addAction(MOVE_TO, x, y);
+ },
+ lineTo: function(x, y) {
+ addAction(LINE_TO, x, y);
+ },
+
+ // for major operations like stroke/fill, we skip compression to ensure
+ // that there are no artifacts at the right edge.
+ stroke: function() { flushActions(true); context.stroke(); },
+ fill: function() { flushActions(true); context.fill(); },
+ beginPath: function() { flushActions(true); context.beginPath(); },
+ closePath: function() { flushActions(true); context.closePath(); },
+
+ _count: function() { return actionCount; }
+ };
+};
+