如何绘制填充多边形？

Question

如何在Android中绘制填充多边形？

Answer 1

Android 没有像 Java 这样方便的 drawPolygon(x_array, y_array, numberofpoints) 操作。您必须逐点制作Path 对象。例如，要为 3D 地牢墙制作填充梯形，您可以将所有点放在 x 和 y 数组中，然后编码如下：

Paint wallpaint = new Paint();
wallpaint.setColor(Color.GRAY);
wallpaint.setStyle(Style.FILL);

Path wallpath = new Path();
wallpath.reset(); // only needed when reusing this path for a new build
wallpath.moveTo(x[0], y[0]); // used for first point
wallpath.lineTo(x[1], y[1]);
wallpath.lineTo(x[2], y[2]);
wallpath.lineTo(x[3], y[3]);
wallpath.lineTo(x[0], y[0]); // there is a setLastPoint action but i found it not to work as expected

canvas.drawPath(wallpath, wallpaint);

要为某个深度添加恒定的线性渐变，您可以编写如下代码。注意 y[0] 使用了两次来保持渐变水平：

 wallPaint.reset(); // precaution when resusing Paint object, here shader replaces solid GRAY anyway
 wallPaint.setShader(new LinearGradient(x[0], y[0], x[1], y[0], Color.GRAY, Color.DKGRAY,TileMode.CLAMP)); 

 canvas.drawPath(wallpath, wallpaint);

请参阅 Paint、Path 和 Canvas 文档了解更多选项，例如数组定义的渐变、添加弧线以及在多边形上放置位图。

Answer 2

您需要将绘制对象设置为 FILL

Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);

然后你可以画任何你想要的东西，它就会被填满。

canvas.drawCircle(20, 20, 15, paint);
canvas.drawRectangle(60, 20, 15, paint);

等等

对于更复杂的形状，您需要使用PATH object。

Answer 3

我喜欢分三步完成...

第 1 步。创建一个尖锐的类 ;-)

/**
 * Simple point
 */
private class Point {

    public float x = 0;
    public float y = 0;

    public Point(float x, float y) {
        this.x = x;
        this.y = y;
    }
}

第 2 步。添加绘图方法/函数

/**
 * Draw polygon
 *
 * @param canvas The canvas to draw on
 * @param color  Integer representing a fill color (see http://developer.android.com/reference/android/graphics/Color.html)
 * @param points Polygon corner points
 */
private void drawPoly(Canvas canvas, int color, Point[] points) {
    // line at minimum...
    if (points.length < 2) {
        return;
    }

    // paint
    Paint polyPaint = new Paint();
    polyPaint.setColor(color);
    polyPaint.setStyle(Style.FILL);

    // path
    Path polyPath = new Path();
    polyPath.moveTo(points[0].x, points[0].y);
    int i, len;
    len = points.length;
    for (i = 0; i < len; i++) {
        polyPath.lineTo(points[i].x, points[i].y);
    }
    polyPath.lineTo(points[0].x, points[0].y);

    // draw
    canvas.drawPath(polyPath, polyPaint);
}

第 3 步。绘制

    drawPoly(canvas, 0xFF5555ee,
            new Point[]{
                new Point(10, 10),
                new Point(15, 10),
                new Point(15, 20)
            });

是的，你可能会更有效地做到这一点，但可能不会更易读:-)。

Answer 4

绘制具有 x 边和自定义半径的多边形：

private void drawPolygon(Canvas mCanvas, float x, float y, float radius, float sides, float startAngle, boolean anticlockwise, Paint paint) {

    if (sides < 3) { return; }

    float a = ((float) Math.PI *2) / sides * (anticlockwise ? -1 : 1);
    mCanvas.save();
    mCanvas.translate(x, y);
    mCanvas.rotate(startAngle);
    Path path = new Path();
    path.moveTo(radius, 0);
    for(int i = 1; i < sides; i++) {
        path.lineTo(radius * (float) Math.cos(a * i), radius * (float) Math.sin(a * i));
    }
    path.close();
    mCanvas.drawPath(path, paint);
    mCanvas.restore();
}

Answer 5

顺便说一句 - 我发现一旦您开始创建路径，路径中的任何 moveTo 命令都将意味着该形状未填充。

仔细想想，Android/Java 会留下未填充的形状是有道理的，因为 moveTo 将代表多边形中的中断。

不过我看过一些这样的教程How to draw a filled triangle in android canvas?

在每个 lineTo 之后都有 moveTo。尽管这可能会导致多边形不中断，但 Android 仍假定 moveTo 表示多边形中的中断。

Answer 6

老问题，但对任何发现这个问题的人来说都是一个技巧。如果您包含具有所需多边形的字体作为字形，则可以使用 drawText 函数来绘制多边形。

缺点是你必须提前知道你需要什么形状。好处是如果你提前知道你可以包含一个漂亮的形状库。此代码假定您在项目的 assets/fonts 文件夹中有一个名为 shape 的字体。

            TypeFace shapesTypeFace = Typeface.createFromAsset(getAssets(), "fonts/shapes.ttf");
            Paint stopSignPaint = new Paint();
            stopSignPaint.setColor(Color.RED);
            //set anti-aliasing so it looks nice
            stopSignPaint.setAntiAlias(true);
            stopSignPaint.setTextSize(200);
            stopSignPaint.setTypeface(shapesTypeFace);

            //will show up as a box or question mark since 
            //the current display font doesn't have this glyph. 
            //open the shapes font in a tool like Character Map 
            //to copy and paste the glyph into your IDE
            //saving it as a variable makes it much easier to work with
            String hexagonGlyph = ""
            String triangleGlyph = ""


            ....whatever code you got...


            //arguments: text, x coordinate, y coordinate, paint
             canvas.drawText(hexagonGlyph, 200, 100, stopSignPaint);

            //make it into a go sign
            stopSignPaint.setColor(Color.Green);
             canvas.drawText(hexagonGlyph, 200, 100, stopSignPaint);


            //make a tiny one
            stopSignPaint.setTextSize(20);
            stopSignPaint.setColor(Color.RED);
             canvas.drawText(hexagonGlyph, 200, 100, stopSignPaint);


             //make a triangle
             canvas.drawText(triangleGlyph, 200, 100, stopSignPaint);

Answer 7

试试这个，或者see the full demo

    Paint paint = new Paint();
    paint.setColor(Color.parseColor("#BAB399"));
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));

Answer 8

这个类可以用来绘制任何类型的多边形。只需在 onDraw() 方法中调用drawPolygonPath()。

class PolygonView : View {
    constructor(context: Context?) : super(context) {
        init()
    }

    constructor(context: Context?, attrs: AttributeSet?) : super(context, attrs) {
        init()
    }

    constructor(context: Context?, attrs: AttributeSet?, defStyleAttr: Int) : super(
        context,
        attrs,
        defStyleAttr
    ) {
        init()
    }

    private lateinit var paint: Paint

    private fun init() {
        paint = Paint().apply {
            color = Color.RED
            isAntiAlias = true
            style = Paint.Style.FILL
            strokeWidth = 10f
        }
    }


    override fun onDraw(canvas: Canvas) {
        canvas.drawPath(drawPolygonPath(8, 150f), paint)
        canvas.drawPath(drawPolygonPath(5, 120f), paint)

    }

    /**
     * @param sides number of polygon sides
     * @param radius side length.
     * @param cx drawing x start point.
     * @param cy drawing y start point.
     * */
    private fun drawPolygonPath(
        sides: Int,
        radius: Float,
        cx: Float = radius,
        cy: Float = radius
    ): Path {
        val path = Path()
        val x0 = cx + (radius * cos(0.0).toFloat())
        val y0 = cy + (radius * sin(0.0).toFloat())
        //2.0 * Math.PI = 2π, which means one circle(360)
        //The polygon total angles of the sides must equal 360 degree.
        val angle = 2 * Math.PI / sides

        path.moveTo(x0, y0)

        for (s in 1 until sides) {

            path.lineTo(
                cx + (radius * cos(angle * s)).toFloat(),
                cy + (radius * sin(angle * s)).toFloat()
            )
        }

        path.close()

        return path
    }
}