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我做的HTML畫布一些工作，我發現，當我畫一條線，我無法清除或繪製了呢？HTML畫布繪製清晰的線條
所以我在做什麼：我有一個網格畫布，其中每個單元格繪製自己（一個填充的矩形，完成頁面加載），當鼠標在網格上時，鼠標所在的單元格應概述（在畫布上繪製四行不再重繪）。當鼠標移動到不同的小區中的新的小區應當概述（如前）和先前概述的細胞不應再被概述（意圖是重繪細胞，畫在線）。這是'未概述'被證明是問題的細胞。
我以爲這與畫家的算法工作，即在畫布上繪製的最後一件事是可見的，但我發現效果表明，填充形狀和線條都具有更高的層上線分開處理？
這裏的來源一個獨立的頁面進行論證：
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
var CANVAS_DIMENSION = 200;
var CANVAS_WIDTH = 10;
var CANVAS_HEIGHT = 10;
var GRID_CELL_WIDTH = CANVAS_DIMENSION/CANVAS_WIDTH;
var GRID_CELL_HEIGHT = CANVAS_DIMENSION/CANVAS_HEIGHT;
var canvas;
var context;
var grid;
var mouseCellColumn = -1;
var mouseCellRow = -1;
function init()
{
canvas = document.getElementById("myCanvas");
context = canvas.getContext("2d");
canvas.addEventListener('mousemove', updateMousePosition, false);
grid = new Array(CANVAS_WIDTH);
for (var i = 0; i < CANVAS_WIDTH; ++i)
{
grid[i] = new Array(CANVAS_HEIGHT);
for (var j = 0; j < CANVAS_HEIGHT; ++j)
{
grid[i][j] = "#0000FF";
}
}
renderScene()
}
function updateMousePosition(event)
{
var initialColumn = mouseCellColumn;
var initialRow = mouseCellRow;
var objectPosition = findPos(this);
var gridPosition = new Point(event.pageX - objectPosition.x, event.pageY - objectPosition.y);
mouseCellColumn = getColumn(gridPosition.x);
mouseCellRow = getRow(gridPosition.y);
var cell_position = getCellPosition(mouseCellColumn, mouseCellRow);
// outline the current cell
drawRectangleOutlineWithColour(cell_position.x,
cell_position.y,
GRID_CELL_WIDTH,
GRID_CELL_HEIGHT,
"#FF0000");
// if mouse has moved cell redraw
if (((initialColumn != mouseCellColumn) ||
(initialRow != mouseCellRow)) &&
(initialColumn > -1) &&
(initialRow > -1))
{
renderGridCell(initialColumn, initialRow);
}
}
function renderScene()
{
for (var i = 0; i < CANVAS_WIDTH; ++i)
{
for (var j = 0; j < CANVAS_HEIGHT; ++j)
{
renderGridCell(i, j);
}
}
}
function renderGridCell(Column, Row)
{
var position = getCellPosition(Column, Row);
drawRectangleWithColour(position.x,
position.y,
GRID_CELL_WIDTH,
GRID_CELL_HEIGHT,
grid[Column][Row]);
}
function drawRectangleWithColour(minX, minY, width, height, colour)
{
context.fillStyle = colour;
context.fillRect(minX,
minY,
width,
height);
}
function drawRectangleOutlineWithColour(minX, minY, width, height, colour)
{
context.strokeStyle = colour;
context.moveTo(minX, minY);
context.lineTo(minX + width, minY);
context.moveTo(minX + width, minY);
context.lineTo(minX + width, minY + height);
context.moveTo(minX + width, minY + height);
context.lineTo(minX, minY + height);
context.moveTo(minX, minY + height);
context.lineTo(minX, minY);
context.stroke();
}
function Point(x, y)
{
this.x = x;
this.y = y;
}
function getColumn(xPosition)
{
if (xPosition < 0)
{
xPosition = 0;
}
if (xPosition > CANVAS_DIMENSION)
{
xPosition = CANVAS_DIMENSION;
}
return Math.floor(xPosition/GRID_CELL_WIDTH);
}
function getRow(yPosition)
{
if (yPosition < 0)
{
yPosition = 0;
}
if (yPosition > CANVAS_DIMENSION)
{
yPosition = CANVAS_DIMENSION;
}
return Math.floor(yPosition/GRID_CELL_HEIGHT);
}
function getCellPosition(column, row)
{
if (row < 0)
{
row = 0;
}
if (row > CANVAS_HEIGHT)
{
row = CANVAS_HEIGHT - 1;
}
if (column < 0)
{
row = 0;
}
if (column > CANVAS_WIDTH)
{
column = CANVAS_WIDTH - 1;
}
var result = new Point(column * GRID_CELL_WIDTH, row * GRID_CELL_HEIGHT);
return result;
}
function findPos(obj)
{
var result = new Point(0, 0);
if (obj.offsetParent)
{
do
{
result.x += obj.offsetLeft;
result.y += obj.offsetTop;
} while (obj = obj.offsetParent);
}
return result;
}
</script>
</head>
<body onload="init()">
<div id="test" style="width: 200px; height:200px; margin: 0px auto;">
<canvas id="myCanvas" width="200" height="200">
Your browser does not support the canvas element.
</canvas>
</div>
</body>
</html>
有問題的區域是在這裏：
// outline the current cell
drawRectangleOutlineWithColour(cell_position.x,
cell_position.y,
GRID_CELL_WIDTH,
GRID_CELL_HEIGHT,
"#FF0000");
// if mouse has moved cell redraw
if (((initialColumn != mouseCellColumn) ||
(initialRow != mouseCellRow)) &&
(initialColumn > -1) &&
(initialRow > -1))
{
renderGridCell(initialColumn, initialRow);
}
，沒有任何效果，輪廓積累。
一些挖掘到畫布上重繪建議「clearRect」但這似乎並沒有幫助，輪廓堅持：
// outline the current cell
drawRectangleOutlineWithColour(cell_position.x,
cell_position.y,
GRID_CELL_WIDTH,
GRID_CELL_HEIGHT,
"#FF0000");
// if mouse has moved cell redraw
if (((initialColumn != mouseCellColumn) ||
(initialRow != mouseCellRow)) &&
(initialColumn > -1) &&
(initialRow > -1))
{
context.clearRect(position.x,
position.y,
GRID_CELL_WIDTH,
GRID_CELL_HEIGHT);
renderGridCell(initialColumn, initialRow);
}
讓我們具體重繪外形部位用不同的顏色？
// outline the current cell
drawRectangleOutlineWithColour(cell_position.x,
cell_position.y,
GRID_CELL_WIDTH,
GRID_CELL_HEIGHT,
"#FF0000");
// if mouse has moved cell redraw
if (((initialColumn != mouseCellColumn) ||
(initialRow != mouseCellRow)) &&
(initialColumn > -1) &&
(initialRow > -1))
{
var position = getCellPosition(initialColumn, initialRow);
drawRectangleWithColour(position.x,
position.y,
GRID_CELL_WIDTH,
GRID_CELL_HEIGHT,
"#00FF00");
}
不，網格重繪，但它對線條沒有影響。重新繪製整個網格？
renderScene();
// outline the current cell
drawRectangleOutlineWithColour(cell_position.x,
cell_position.y,
GRID_CELL_WIDTH,
GRID_CELL_HEIGHT,
"#FF0000");
/*
// if mouse has moved cell redraw
if (((initialColumn != mouseCellColumn) ||
(initialRow != mouseCellRow)) &&
(initialColumn > -1) &&
(initialRow > -1))
{
var position = getCellPosition(initialColumn, initialRow);
drawRectangleWithColour(position.x,
position.y,
GRID_CELL_WIDTH,
GRID_CELL_HEIGHT,
"#00FF00");
}
*/
我似乎無法找到的畫布是如何處理這個，我得到的Safari MacOSX上與Chrome和Firefox上的Windows7相同的行爲一個很好的解釋。
感謝這個整理，並感謝完美像素的東西太多。 – Paddy 2012-07-20 21:31:40