javascript - 缩放/平移后的 Canvas 坐标

Question

我正在根据从 api 接收到的一些数据构建 Canvas，这一切都很好。无论如何，有几天我坚持使用以下代码`canvas.addEventListener('wheel', (event: MouseWheelEvent) => { event.preventDefault();

    let coords = Positioning.transformedPoint(
      event.pageX - canvas.offsetLeft,
      event.pageY - canvas.offsetTop
    );

    canvasMethods.clear();
    canvasMethods.translate(coords.x, coords.y);

    if (event.wheelDeltaY > 0) {
      canvasMethods.scale(ZoomDirection.ZOOM_IN);
    } else if (event.wheelDeltaY < 0) {
      canvasMethods.scale(ZoomDirection.ZOOM_OUT);
    }

    canvasMethods.translate(-coords.x, -coords.y);

    this._renderFn();
  }, false);

  canvas.addEventListener('mousedown', (event: MouseEvent) => {
    event.preventDefault();

    this._dragging = true;
    this._dragStart = Positioning.transformedPoint(
      event.clientX - canvas.offsetLeft,
      event.clientY - canvas.offsetTop
    );
  }, false);

  canvas.addEventListener('dblclick', (event: MouseEvent) => {
    let coords = Positioning.transformedPoint(
      event.clientX - canvas.offsetLeft,
      event.clientY - canvas.offsetTop
    );
    this._clickFn(coords);
  });

  canvas.addEventListener('mousemove', (event: MouseEvent) => {
    if (this._dragging) {
      event.preventDefault();

      this._dragEnd = Positioning.transformedPoint(
        event.pageX - canvas.offsetLeft,
        event.pageY - canvas.offsetTop
      );

      let coords = Positioning.transformedPoint(
        event.clientX - canvas.offsetLeft,
        event.clientY - canvas.offsetTop
      );

      canvasMethods.translate(coords.x - this._dragStart.x, coords.y - this._dragStart.y);
      canvasMethods.clear();

      this._renderFn();
      this._dragStart = this._dragEnd;
    }
  }, false);

  canvas.addEventListener('mouseup', (event: MouseEvent) => {
    event.preventDefault();

    this._dragging = false;
    this._dragStart = null;
    this._dragEnd = null;
  })
}`

当它处于正常比例时，我得到了正确的坐标，但是当我缩放时，我得到了一个增量错误(基本上实际点和鼠标光标之间的距离越来越大)，我不知道为什么。为了计算矩阵中的坐标，我按以下方式使用 SVG 方法作为包装器`export class Positioning { static svg = document.createElementNS(' http://www.w3.org/2000/svg ', 'svg'); private static xform = Positioning.svg.createSVGMatrix();

static transformedPoint(x: number, y: number): SVGPoint {
  let coords = Positioning.svg.createSVGPoint();

  coords.x = x;
  coords.y = y;

  return coords.matrixTransform(Positioning.xform.inverse());
}

}`

我知道这在某种程度上与缩放有关，但我真的不知道如何计算缩放比例并进行适当的操作以获得比例。我也检查了这个答案 Zoom Canvas to Mouse Cursor这是相当准确的，但实际上他以某种我无法重新认识的方式得到了它。其他人遇到过同样的问题吗？

Answer 1

我已经解决了这个问题，我忘记了一个重要的东西来跟踪我的转变。现在我将链接代码以供可能遇到我同样问题的人使用(如果您不使用 Typescript 可以避免输入 ofc)

基本上我使用 SVG 矩阵方法来追踪 Canvas 中发生的事情。

这是一个通过在自身中存储由 createSVGMatrix() 创建的未转换 Canvas (1,0,0,1,0,0) 的基本矩阵并通过 native SVGMatrix 方法跟踪转换来获取 Canvas 转换的类正在更新原始矩阵。然后，当我需要时，我只需使用转换点方法来恢复鼠标的正确 x、y 坐标，按比例缩放到矩阵。

export class Positioning {
static svg = document.createElementNS('http://www.w3.org/2000/svg', 'svg');
static MatrixTransformationProxy = Positioning.svg.createSVGMatrix();

static transformedPoint(x: number, y: number): SVGPoint {
  let coords = Positioning.svg.createSVGPoint();

  coords.x = x;
  coords.y = y;

  return coords.matrixTransform(Positioning.MatrixTransformationProxy.inverse());
}

static translateProxy(x: number, y: number) {
  Positioning.MatrixTransformationProxy = Positioning.MatrixTransformationProxy.translate(x, y);
}

static scaleUniformProxy(scaleValue: number) {
  Positioning.MatrixTransformationProxy = Positioning.MatrixTransformationProxy.scale(scaleValue);
}

我使用调用 Canvas 方法和相对 Positioning 方法的 Canvas 方法包装器使我的 Canvas 转换与我的 ProxyMatrix 保持同步，像这样更新 MatrixTransformationProxy

export class CanvasMethods {
static getSharedInstance(): CanvasMethods {
  return sharedInstance;
}

private _canvas: HTMLCanvasElement;

getCanvas(): HTMLCanvasElement {
  return this._canvas;
}

getContext(): CanvasRenderingContext2D {
  return this._canvas.getContext('2d');
}

registerCanvas(canvas: HTMLCanvasElement): void {
  this._canvas = canvas;
}

getCanvasBoundingRect(): BoundingRect {
  return new BoundingRect(0, 0, this._canvas.width, this._canvas.height);
}

clear(): void {
  this.getContext().save();
  this.getContext().setTransform(1, 0, 0, 1, 0, 0);
  this.getContext().clearRect(0, 0, this._canvas.width, this._canvas.height);
  this.getContext().restore();
}

scale(direction: ZoomDirection): void {
  let options = { //TODO get this from constructor options
    scaleValueOut: 0.8,
    scaleValueIn: 1.1
  };

  if (direction === ZoomDirection.ZOOM_OUT) {
    Positioning.scaleUniformProxy(options.scaleValueOut);
    this.getContext().scale(options.scaleValueOut, options.scaleValueOut);
  } else if (direction === ZoomDirection.ZOOM_IN) {
    Positioning.scaleUniformProxy(options.scaleValueIn);
    this.getContext().scale(options.scaleValueIn, options.scaleValueIn);
  }
}

translate(x: number, y: number): void {
  Positioning.translateProxy(x, y);
  this.getContext().translate(x, y);
}

const sharedInstance = new CanvasMethods();