Android绘制球轨迹

Question

我的应用程序中有球只是飞过显示器.他们画出我想要的.但现在我想在他们身后画出一条痕迹.

我所能做的只是画canvas.drawPath下面的图片:

但这不是我想要的.它应该有尖尾和渐变颜色,如下所示:

我不知道怎么做.尝试过BitmapShader- 无法做出正确的事情.请帮忙.

码:

首先,有一个Point显示位置的类:

class Point {
    float x, y;
    ...
}

并且跟踪存储为以下队列Point:

private ConcurrentLinkedQueue<Point> trail;

它如何填充并不重要,只要知道它有大小限制:

trail.add(position);
if(trail.size() > TRAIL_MAX_COUNT) {
    trail.remove();
}

绘图发生在DrawTrail方法中:

private void DrawTrail(Canvas canvas) {
    trailPath.reset();
    boolean isFirst = true;
    for(Point p : trail) {
        if(isFirst) {
            trailPath.moveTo(p.x, p.y);
            isFirst = false;
        } else {
            trailPath.lineTo(p.x, p.y);
        }
    }
    canvas.drawPath(trailPath, trailPaint);
}

顺便说一下,trailPaint真是胖油漆:)

trailPaint = new Paint();
trailPaint.setStyle(Paint.Style.STROKE);
trailPaint.setColor(color);
trailPaint.setStrokeWidth(radius * 2);
trailPaint.setAlpha(150);

Answer 1

我找到了解决方案。但还是觉得这不是最好的。

首先，我的类字段用于该任务。

static final int TRAIL_MAX_COUNT = 50; //maximum trail array size
static final int TRAIL_DRAW_POINT = 30; //number of points to split the trail for draw

private ConcurrentLinkedQueue<Point> trail;
private Paint[] trailPaints;
private float[][] trailPoss, trailTans;
private Path trailPath;

除了trailPath对象之外，我还使用PathMeasure对象将路径分割为多个相等的部分。

填充轨迹数组对象后添加了轨迹计算函数的调用。

lastTrailAdd = now;
trail.add(pos.Copy());
if (trail.size() > TRAIL_MAX_COUNT) {
    trail.remove();
}
FillTrail();

然后是我的FillTrail功能。

private void FillTrail() {
    trailPath.reset();
    boolean isFirst = true;
    for(Point p : trail) {
        if(isFirst) {
            trailPath.moveTo(p.x, p.y);
            trailPoss[0][0] = p.x;
            trailPoss[0][1] = p.y;
            isFirst = false;
        } else {
            trailPath.lineTo(p.x, p.y);
        }
    }
    PathMeasure path = new PathMeasure(trailPath, false);
    float step = path.getLength() / TRAIL_DRAW_POINT;
    for(int i=0; i<TRAIL_DRAW_POINT; i++) {
        path.getPosTan(step * i, trailPoss[i], trailTans[i]);
    }
}

它与拉丝线分离。下一个代码是绘图函数。

private void DrawTrail(Canvas canvas) {
    if(trail.size() > 1) {
        float prevWidthHalfX = 0f, prevWidthHalfY = 0f, prevX = 0f, prevY = 0f;
        Path trailStepRect = new Path();
        boolean isFirst = true;
        for (int i = 0; i < TRAIL_DRAW_POINT; i++) {
            float currWidthHalf = (float) (radius) * i / TRAIL_DRAW_POINT / 2f,
                    currWidthHalfX = currWidthHalf * trailTans[i][1],
                    currWidthHalfY = currWidthHalf * trailTans[i][0],
                    currX = trailPoss[i][0], currY = trailPoss[i][1];
            if (!isFirst) {
                trailStepRect.reset();
                trailStepRect.moveTo(prevX - prevWidthHalfX, prevY + prevWidthHalfY);
                trailStepRect.lineTo(prevX + prevWidthHalfX, prevY - prevWidthHalfY);
                trailStepRect.lineTo(currX + currWidthHalfX, currY - currWidthHalfY);
                trailStepRect.lineTo(currX - currWidthHalfX, currY + currWidthHalfY);
                canvas.drawPath(trailStepRect, trailPaints[i]);
            } else {
                isFirst = false;
            }
            prevX = currX;
            prevY = currY;
            prevWidthHalfX = currWidthHalfX;
            prevWidthHalfY = currWidthHalfY;
        }
    }
}

其要点是用不同的油漆绘制零件的痕迹。离球越近 - 轨迹越宽。我想我会优化它，但这已经是工作了。

如果您想观看它的外观，只需从 google play 安装我的应用程序即可。