Question

我试图在画布上渲染SVG图像，一次一个地绘制图像以填充给定的行，下面是相同的代码片段：

z = {}
y = df.iloc[0:100, 4].values
z['spam'] = np.where(y == 'spam', -1, 1)

问题是我可以看到部分填充的行，我不想要，有没有办法一次填满整行？

Answer 1

是。首先将整行瓷砖绘制到屏幕外的Canvas。完成后，您可以将该屏幕外画布绘制到主画布上。

类似的东西：

var offscreenCanvas = document.createElement('canvas');
offscreenCanvas .width = <whatever>;
offscreenCanvas .height = <whatever>;
var offscreenContext = offscreenCanvas.getContext('2d');

// Draw all your tiles
renderSVGTile(offscreenContext, svg, pos);
//... loop through all tiles etc

// When finished...
mainCanvasContext.drawImage(offscreenCanvas, 0, 0);

演示：

＆＃13;

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var image = document.getElementById("source");

var offscreenCanvas = document.createElement("canvas");
offscreenCanvas.width = 300;
offscreenCanvas.height = 150;
var offscreenContext = offscreenCanvas.getContext("2d");

offscreenContext.drawImage(image, 33, 71, 104, 124, 21, 20, 87, 104);
offscreenContext.drawImage(image, 33, 71, 104, 124, 108, 20, 87, 104);

ctx.drawImage(offscreenCanvas, 0, 0);

＆＃13;

<canvas id="canvas"></canvas>
<div style="display:none;">
  <img id="source" src="http://placekitten.com/300/227"
       width="300" height="227">
</div>

＆＃13;

Answer 2

我就是这样做的，虽然我不确定它是否能满足你的目的，因为我在渲染时在文档中有图像，它只是隐藏。

var ctx = document.getElementById("canvasID").getContext("2d");
ctx.drawImage(document.getElementById("imageID"), x,y,w,h);

Answer 3

以下解决方案对我来说很好：

 /**
   * @param {CanvasRenderingContext2D} ctx
   * @param {!Array<!SVGTile>} tiles
   */
  function drawTiles(ctx, tiles) {
    var canvas  = document.createElement('canvas');
    var width   = tiles.length * TILE_WIDTH;
    var height  = TILE_HEIGHT;
    var y = tiles[0].y;
    canvas.width  = tiles.length * TILE_WIDTH;
    canvas.height = TILE_HEIGHT;
    var context = canvas.getContext("2d");
    tiles.forEach(function(tile, index) {
      renderTile(context, tile, function() {
        if (tiles.length === index + 1) {
          ctx.drawImage(canvas, 0, y);
        }
      });
    });
    // TODO: Below code is for testing purpose.
    var temp = document.createElement('div');
    temp.appendChild(canvas);
    document.body.appendChild(temp);
  };


  /**
   * Renders svg tile on the given context.
   * @param {CanvasRenderingContext2D} ctx
   * @param {!Tile} tile The tile to render.
   * @param {function()} callback To be called after image is loaded.
   * @throws Error
   */
  function renderTile(ctx, tile, callback) {
    var img = new Image();
    img.onload = function() {
      try {
        ctx.drawImage(this, tile.x, 0, tile.width, tile.height);
        ctx.imageSmoothingEnabled = false;
        ctx.mozImageSmoothingEnabled = false;
        DOMURL.revokeObjectURL(tile.svgURL);
        callback();
      } catch (e) {
        throw new Error('Could not render image' + e);
      }
    };
    img.src = tile.svgURL;
  };

在画布上渲染svg图像

3 个答案: