HTML5 Canvas实现放大镜效果示例

鼠标移动到放大镜上，然后按下鼠标左键，可以拖动放大镜，不按鼠标左键或者不在放大镜区域都不可以拖动放大镜。
为了实现上面的效果，我们要实现3种事件 mousedown, mousemove, 'mouseup', 当鼠标按下时，检测是否在放大镜区域，如果在，设置放大镜可以移动。鼠标移动时更新放大镜中兴点的坐标。鼠标松开时，设置放大镜不可以被移动。

canvas.onmousedown = function (e) { var point = windowToCanvas(e.clientX, e.clientY); var x1, x2, y1, y2, dis; x1 = point.x; y1 = point.y; x2 = centerPoint.x; y2 = centerPoint.y; dis = Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2); if (dis < Math.pow(originalRadius, 2)) { lastPoint.x = point.x; lastPoint.y = point.y; moveGlass = true; } } canvas.onmousemove = function (e) { if (moveGlass) { var xDis, yDis; var point = windowToCanvas(e.clientX, e.clientY); xDis = point.x - lastPoint.x; yDis = point.y - lastPoint.y; centerPoint.x += xDis; centerPoint.y += yDis; lastPoint.x = point.x; lastPoint.y = point.y; draw(); } } canvas.onmouseup = function (e) { moveGlass = false; }

鼠标双击

当移动到对应的线段上时，鼠标双击可以选择该线段，将该线段的颜色变为红色。

canvas.ondblclick = function (e) { var xStart, xEnd, yStart, yEnd; var clickPoint = {}; clickPoint.x = scaleGlassRectangle.x + scaleGlassRectangle.width / 2; clickPoint.y = scaleGlassRectangle.y + scaleGlassRectangle.height / 2; var index = -1; for (var i = 0; i < scaleGlassLines.length; i++) { var scaleLine = scaleGlassLines[i]; xStart = scaleGlassRectangle.x + scaleLine.xStart - 3; xEnd = scaleGlassRectangle.x + scaleLine.xStart + 3; yStart = scaleGlassRectangle.y + scaleLine.yStart; yEnd = scaleGlassRectangle.y + scaleLine.yEnd; if (clickPoint.x > xStart && clickPoint.x < xEnd && clickPoint.y < yStart && clickPoint.y > yEnd) { scaleLine.color = "#f00"; index = scaleLine.index; break; } } for (var i = 0; i < chartLines.length; i++) { var line = chartLines[i]; if (line.index == index) { line.color = "#f00"; } else { line.color = "#888"; } } draw(); }

键盘事件

因为线段离得比较近，所以使用鼠标移动很难精确的选中线段，这里使用键盘的w, a, s, d 来进行精确移动

document.onkeyup = function (e) { if (e.key == 'w') { centerPoint.y = intAdd(centerPoint.y, -0.2); } if (e.key == 'a') { centerPoint.x = intAdd(centerPoint.x, -0.2); } if (e.key == 's') { centerPoint.y = intAdd(centerPoint.y, 0.2); } if (e.key == 'd') { centerPoint.x = intAdd(centerPoint.x, 0.2); } draw(); }

** 参考资料 **
HTML5-MagnifyingGlass

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