Android画球轨迹

Question

我的应用程序中有一些球会飞过显示屏。他们按照我的意愿画画。但现在我想画出他们身后的踪迹

我能做的就是画canvas.drawPath像下图这样的东西：

但这不是我想要的。它应该有这样的尖尾巴和渐变色：

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

代码：

首先显示的位置是Point class:

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

轨迹存储为 Point 的 queue:

private ConcurrentLinkedQueue<Point> trail;

不管怎么填，只要知道有大小限制即可：

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 真的很胖:)

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

Answer 1

我知道你想在球的路径上看到一个渐变，你可以使用这样的东西

 int x1 = 0, y1 = 0, x2 = 0,  y2 = 40;
 Shader shader = new LinearGradient(0, 0, 0, 40, Color.WHITE, Color.BLACK, TileMode.CLAMP);
trailPaint = new Paint(); 
trailPaint.setShader(shader);

这就是您应该将 trailPaint 更改为的内容，看看它是否有效。

由here提供。

Answer 2

我找到了解决方案。不过还是觉得不是最好的

首先，我的 class 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 对象将路径拆分为多个相等的部分。

填充轨迹数组对象后添加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函数。

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]);
    }
}

画线分离了。下一个代码是绘图功能。

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;
        }
    }
}

这个的要点是用不同的油漆来绘制轨迹。更接近球 - 更宽的轨迹。我想我会优化它，但它已经准备好了。

如果您想观看它的外观，只需安装 my app from google play。

Android画球轨迹

Android draw ball trail

java

android

drawing