android - Canvas : Path with negative and large positive numbers

Question

在我的 Android 应用程序中，我有一个可以缩放和平移的 View 。在那个观点上，我想为以下几点画一条线。但是根本没有显示路径。我想知道这是否与点列表中的负数或大数有关。

{"x":-317,"y":-744},{"x":50,"y":-702},{"x":394,"y":-663},{"x":718,"y":-626},{"x":1023,"y":-592},{"x":1310,"y":-560},{"x":1581,"y":-529},{"x":1837,"y":-500},{"x":2079,"y":-472},{"x":2951,"y":198},{"x":5997,"y":4780},{"x":4064,"y":4143},{"x":2686,"y":3689},{"x":1654,"y":3348},{"x":852,"y":3084},{"x":211,"y":2873},{"x":-312,"y":2700},{"x":-748,"y":2556},{"x":-895,"y":2213},{"x":-574,"y":569},{"x":-317,"y":-744}]}

这是代码 fragment 。

private final Paint paintStrokeArea = new Paint(Paint.ANTI_ALIAS_FLAG);
private Point[] viewArea = ...

public MyView(Context context, AttributeSet attributeSet) {
    super(context, attributeSet);

    paintStrokeArea.setColor(Color.WHITE);
    paintStrokeArea.setStyle(Style.STROKE);
    paintStrokeArea.setStrokeWidth(4.5f);
    paintStrokeArea.setStrokeJoin(Join.MITER);
    paintStrokeArea.setPathEffect(null);
}

public onDraw(Canvas) {
    if (viewArea != null)
        renderViewArea(viewArea, canvas, paintStroke);
}

public static void renderViewArea(Point[] area, Canvas canvas, Paint paint) {
    if (area == null || canvas == null || paint == null)
        return;

    boolean first = true;
    Path path = new Path();
    Point last = new Point();

    for (Point current : area) {
        if (first) {
            first = false;
        } else {
            path.moveTo(last.x, last.y);
            path.lineTo(current.x, current.y);
        }

        last.set(current.x, current.y);
    }

    if (!first)
        canvas.drawPath(path, paint);
}

Answer 1

this post 中描述了同样的问题.根据答案，出现问题是因为 drawPath 是在 CPU 中通过将其渲染成位图然后传输到 GPU 中来完成的。因为我的路径太大，位图无法渲染(发送到)GPU。最好使用 drawLines，因为它直接使用 GPU。这是我封装的辅助类。

package eu.level12.tools;

import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Point;

/**
 * Provides several static methods for drawing onto Android's canvas.
 * Hardware-accelerated methods are named with the prefix render while others
 * begin with draw.
 * 
 * @author Matthias Heise
 * 
 */
public final class DrawingTools {

    /**
     * Draws the line specified by the given path using hardware-accelerated
     * method Canvas.drawLines. Has no effect if either argument is null or if
     * the line consists of less than two points.
     * 
     * @param path
     *            A path of points that specifies the line.
     * @param canvas
     *            The canvas onto which the line should be drawn.
     * @param paint
     *            The paint argument that specifies how the line is drawn.
     */
    public static void renderLine(Point[] path, Canvas canvas, Paint paint) {

        if (path == null || canvas == null || paint == null || path.length <= 1)
            return;

        final float[] lines = new float[(path.length - 1) * 4];
        int index = 0;
        final Point last = new Point();
        boolean first = true;

        for (Point current : path) {
            if (first) {
                first = false;
            } else {

                // start point
                lines[index] = last.x;
                lines[index + 1] = last.y;

                // end point
                lines[index + 2] = current.x;
                lines[index + 3] = current.y;

                index += 4;
            }

            last.set(current.x, current.y);
        }

        if (!first)
            canvas.drawLines(lines, paint);
    }
}