在画布上画一颗心

Question

我想在 Canvas 上画一个心形。我发现了不同的数学方程，但我无法将它们中的任何一个转换为我可以在 onDraw 方法中实现的代码。我希望在这里有一颗类似这种形状的心：

我所追求的形状方程：

Answer 1

Android 绘图 API 不提供用于绘制任意方程曲线的工具。如果您愿意脱离为心脏找到的特定功能形式，您可以使用 api 支持的三次贝塞尔曲线绘制心脏（没有颜色效果）。您将创建一个Path，然后使用其cubicTo 方法添加曲线部分。然后您将使用Canvas#drawPath 渲染Path。

要使用三次贝塞尔曲线获得心形，请查看this example（恰好在 JavaScript 中，但这个想法应该很容易移植到 Android）。

我不确定在心形中创建颜色渐变的最佳方法是什么。我的建议是使用贝塞尔曲线定义心脏的内边界和外边界，并将其设置为Paint 的剪辑区域。然后，您可以使用 Paint 进行渐变填充，以限制绘制渐变的位置。

Answer 2

public class HeartShape extends FrameLayout {

    private Paint paint;
    public HeartShape(@NonNull Context context) {
        super(context);
        init();
    }

    private void init() {
        paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(Color.RED);
        paint.setStyle(Style.STROKE);
        setWillNotDraw(false);
    }

    public HeartShape(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public HeartShape(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    public HeartShape(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init();
    }

    @Override
    protected void onDraw(Canvas canvas) {

        Path path = createHeartPath(canvas.getClipBounds().right,canvas.getClipBounds().bottom);

        canvas.drawPath(path,paint);

        super.onDraw(canvas);
    }

    private Path createHeartPath(int width, int height) {
        Path path = new Path();
        path.moveTo(0,height/3f);
        path.lineTo(width,height/3f);
        path.moveTo(width/2f,0f);
        path.lineTo(width/2f,height);

        float pX = width/2f;
        float pY = (height/100f)*33.33f;

        float x1 = (width/100f)*50;
        float y1 = (height/100f)*5;
        float x2 = (width/100f)*90;
        float y2 = (height/100f)*10;
        float x3 = (width/100f)*90;
        float y3 = (height/100f)*33.33f;

        path.moveTo(pX,pY);
        path.cubicTo(x1, y1, x2, y2, x3, y3);
        path.moveTo(x3,pY);

        x1 = (width/100f)*90;
        y1 = (height/100f)*55f;
        x2 = (width/100f)*65;
        y2 = (height/100f)*60f;
        x3 = (width/100f)*50;
        y3 = (height/100f)*90f;

        path.cubicTo(x1, y1, x2, y2, x3, y3);
       // path.lineTo(pX,pY);


        x1 = (width/100f)*50;
        y1 = (height/100f)*5;
        x2 = (width/100f)*10;
        y2 = (height/100f)*10;
        x3 = (width/100f)*10;
        y3 = (height/100f)*33.33f;

        path.moveTo(pX,pY);
        path.cubicTo(x1, y1, x2, y2, x3, y3);
        path.moveTo(x3,pY);

        x1 = (width/100f)*10;
        y1 = (height/100f)*55f;
        x2 = (width/100f)*35f;
        y2 = (height/100f)*60f;
        x3 = (width/100f)*50f;
        y3 = (height/100f)*90f;

        path.cubicTo(x1, y1, x2, y2, x3, y3);
        //path.lineTo(pX,pY);

        path.moveTo(x3,y3);
        path.close();

        return path;
    }


}

Output

去掉画线代码并设置paint.setStyle(Style.FILL);

private Path createHeartPath(int width, int height) {
    Path path = new Path();
   //path.moveTo(0,height/3f);
   //path.lineTo(width,height/3f);
   //path.moveTo(width/2f,0f);
   //path.lineTo(width/2f,height);

    float pX = width/2f;
    float pY = (height/100f)*33.33f;

    float x1 = (width/100f)*50;
    float y1 = (height/100f)*5;
    float x2 = (width/100f)*90;
    float y2 = (height/100f)*10;
    float x3 = (width/100f)*90;
    float y3 = (height/100f)*33.33f;

    path.moveTo(pX,pY);
    path.cubicTo(x1, y1, x2, y2, x3, y3);
    path.moveTo(x3,pY);

    x1 = (width/100f)*90;
    y1 = (height/100f)*55f;
    x2 = (width/100f)*65;
    y2 = (height/100f)*60f;
    x3 = (width/100f)*50;
    y3 = (height/100f)*90f;

    path.cubicTo(x1, y1, x2, y2, x3, y3);
    path.lineTo(pX,pY);


    x1 = (width/100f)*50;
    y1 = (height/100f)*5;
    x2 = (width/100f)*10;
    y2 = (height/100f)*10;
    x3 = (width/100f)*10;
    y3 = (height/100f)*33.33f;

    path.moveTo(pX,pY);
    path.cubicTo(x1, y1, x2, y2, x3, y3);
    path.moveTo(x3,pY);

    x1 = (width/100f)*10;
    y1 = (height/100f)*55f;
    x2 = (width/100f)*35f;
    y2 = (height/100f)*60f;
    x3 = (width/100f)*50f;
    y3 = (height/100f)*90f;

    path.cubicTo(x1, y1, x2, y2, x3, y3);
    path.lineTo(pX,pY);

    path.moveTo(x3,y3);
    path.close();

    return path;
}

我们可以修改createHeartPath()方法的这个逻辑/绘图物理并获得更好的输出，欢迎新的建议和更改。