clip method

bool clip(double x1, double y1, double x2, double y2, double x3, double y3, Float32List clippingArea, Float32List output,)

Implementation

bool clip(double x1, double y1, double x2, double y2, double x3, double y3,
    Float32List clippingArea, Float32List output) {
  final Float32List originalOutput = output;
  bool clipped = false;

  // Avoid copy at the end.
  Float32List input;
  if (clippingArea.length % 4 >= 2) {
    input = output;
    output = scratch as Float32List;
  } else {
    input = scratch as Float32List;
  }

  input
    ..length = 0
    ..add(x1)
    ..add(y1)
    ..add(x2)
    ..add(y2)
    ..add(x3)
    ..add(y3)
    ..add(x1)
    ..add(y1);
  output.length = 0;

  final Float32List clippingVertices = clippingArea;
  final int clippingVerticesLast = clippingArea.length - 4;
  for (int i = 0;; i += 2) {
    final double edgeX = clippingVertices[i], edgeY = clippingVertices[i + 1];
    final double edgeX2 = clippingVertices[i + 2],
        edgeY2 = clippingVertices[i + 3];
    final double deltaX = edgeX - edgeX2, deltaY = edgeY - edgeY2;

    final Float32List inputVertices = input;
    final int inputVerticesLength = input.length - 2,
        outputStart = output.length;
    for (int ii = 0; ii < inputVerticesLength; ii += 2) {
      final double inputX = inputVertices[ii], inputY = inputVertices[ii + 1];
      final double inputX2 = inputVertices[ii + 2],
          inputY2 = inputVertices[ii + 3];
      final bool side2 =
          deltaX * (inputY2 - edgeY2) - deltaY * (inputX2 - edgeX2) > 0;
      if (deltaX * (inputY - edgeY2) - deltaY * (inputX - edgeX2) > 0) {
        if (side2) {
          // v1 inside, v2 inside
          output
            ..add(inputX2)
            ..add(inputY2);
          continue;
        }
        // v1 inside, v2 outside
        final double c0 = inputY2 - inputY, c2 = inputX2 - inputX;
        final double ua = (c2 * (edgeY - inputY) - c0 * (edgeX - inputX)) /
            (c0 * (edgeX2 - edgeX) - c2 * (edgeY2 - edgeY));
        output
          ..add(edgeX + (edgeX2 - edgeX) * ua)
          ..add(edgeY + (edgeY2 - edgeY) * ua);
      } else if (side2) {
        // v1 outside, v2 inside
        final double c0 = inputY2 - inputY, c2 = inputX2 - inputX;
        final double ua = (c2 * (edgeY - inputY) - c0 * (edgeX - inputX)) /
            (c0 * (edgeX2 - edgeX) - c2 * (edgeY2 - edgeY));
        output
          ..add(edgeX + (edgeX2 - edgeX) * ua)
          ..add(edgeY + (edgeY2 - edgeY) * ua)
          ..add(inputX2)
          ..add(inputY2);
      }
      clipped = true;
    }

    if (outputStart == output.length) {
      // All edges outside.
      originalOutput.length = 0;
      return true;
    }

    output
      ..add(output[0])
      ..add(output[1]);

    if (i == clippingVerticesLast) break;
    final Float32List temp = output;
    output = input..length = 0;
    input = temp;
  }

  if (originalOutput != output) {
    originalOutput.length = 0;
    final int n = output.length - 2;
    for (int i = 0; i < n; i++) {
      originalOutput[i] = output[i];
    }
  } else {
    originalOutput.length = originalOutput.length - 2;
  }

  return clipped;
}