一、ComposeShader 组合渲染

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Paint 的 ComposeShader 是 组合渲染 , 可以将两个个 Shader 渲染组合使用 ；

ComposeShader 文档地址 : https://developer.android.google.cn/reference/kotlin/android/graphics/ComposeShader

ComposeShader 组合渲染 需要设置 dst 和 src 两个渲染 , 还有两个渲染的组合模式 , 可以设置 Xfermode / PorterDuff.Mode / BlendMode 三种之一的组合模式 ;

ComposeShader(
    shaderA: Shader, // The colors from this shader are seen as the "dst" by the mode This value cannot be null.
    shaderB: Shader, // The colors from this shader are seen as the "src" by the mode This value cannot be null.
    mode: Xfermode) // The mode that combines the colors from the two shaders. If mode is null, then SRC_OVER is assumed.

ComposeShader(
    shaderA: Shader, // The colors from this shader are seen as the "dst" by the mode This value cannot be null.
    shaderB: Shader, // The colors from this shader are seen as the "src" by the mode This value cannot be null.
    mode: PorterDuff.Mode) // The PorterDuff mode that combines the colors from the two shaders. This value cannot be null.

ComposeShader(
    shaderA: Shader, // The colors from this shader are seen as the "dst" by the mode This value cannot be null.
    shaderB: Shader, // The colors from this shader are seen as the "src" by the mode This value cannot be null.
    blendMode: BlendMode) // The blend mode that combines the colors from the two shaders. This value cannot be null.

二、ComposeShader 组合渲染代码示例

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package kim.hsl.paintgradient.compose;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.ComposeShader;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.RadialGradient;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.SweepGradient;
import android.util.AttributeSet;
import android.view.View;

import androidx.annotation.Nullable;

public class ComposeShaderView extends View {

    /**
     * 画笔工具
     * 线性渐变渲染 需要设置给该 画笔工具
     */
    private Paint mPaint;

    /**
     * 使用线性渐变绘制的区域
     */
    private RectF mRectF;

    public ComposeShaderView(Context context) {
        this(context, null);
    }

    public ComposeShaderView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ComposeShaderView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initPaint();
    }

    @Override
    protected void onSizeChanged(int width, int height, int oldWidth, int oldHeight) {
        super.onSizeChanged(width, height, oldWidth, oldHeight);
    }

    /**
     * 初始化 画笔工具, 主要是设置该画笔的渲染
     */
    private void initPaint() {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setStyle(Paint.Style.FILL);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        SweepGradient sg = new SweepGradient(
                this.getWidth() / 2,
                this.getHeight() / 2,
                Color.RED, Color.YELLOW);

        RadialGradient rg = new RadialGradient(
                this.getWidth() / 2,
                this.getHeight() / 2,
                400,
                Color.GREEN, Color.YELLOW,
                Shader.TileMode.CLAMP);

        ComposeShader cs = new ComposeShader(rg, sg, PorterDuff.Mode.MULTIPLY);


        mPaint.setShader(cs);
        canvas.drawCircle(this.getWidth() / 2, this.getHeight() / 2, 400, mPaint);
    }

}