Android渲染器Shader：LinearGradient（一）

秒速五厘米 2023-10-17 08:04 2阅读 0赞

**Android渲染器Shader：LinearGradient（一）**

LinearGradient是Android的线性渲染器。我写5个LinearGradient渲染器渲染后的View表现结果。其中，LinearGradient 1,2,3只是修改渲染器的渲染模式，LinearGradient 1为重复（repeat），LinearGradient 2为镜像模式（mirror），LinearGradient 3为拉伸（clamp）。注意到LinearGradient 3在拉伸模式下，如果设定的LinearGradient不足以渲染整个画面，那么将拉伸最后一个颜色（我写的这个例子是蓝色Color.BLUE）。  
LinearGradient 4和5则只是为了演示构造LinearGradient的float x0, float y0, float x1, float y1在复杂设置后会形成的画面渲染效果。  
以LinearGradient 4为例，如果设定x0=0，y0=0，x1=300，y1=300，那么就是从左上角往右下角沿这个300 X 300的正方形的左上——右下对称轴渲染。

写一个完整代码。  
先写一个LinearGradientView，这个LinearGradient继承自View：

package zhangphil.demo;
    
    import android.content.Context;
    import android.graphics.Canvas;
    import android.graphics.Color;
    import android.graphics.LinearGradient;
    import android.graphics.Paint;
    import android.graphics.Rect;
    import android.util.AttributeSet;
    import android.graphics.Shader;
    import android.view.View;
    
    public class LinearGradientView extends View {
    
    	private LinearGradient linearGradient1 = null;
    	private Paint paint1 = null;
    
    	private LinearGradient linearGradient2 = null;
    	private Paint paint2 = null;
    
    	private LinearGradient linearGradient3 = null;
    	private Paint paint3 = null;
    
    	private LinearGradient linearGradient4 = null;
    	private Paint paint4 = null;
    
    	private LinearGradient linearGradient5 = null;
    	private Paint paint5 = null;
    
    	public LinearGradientView(Context context) {
    		super(context);
    
    		linearGradient1 = new LinearGradient(0, 0, 300, 0, new int[] { Color.RED, Color.YELLOW, Color.BLUE }, null,
    				Shader.TileMode.REPEAT);
    		paint1 = new Paint();
    
    		linearGradient2 = new LinearGradient(0, 0, 300, 0, new int[] { Color.RED, Color.YELLOW, Color.BLUE }, null,
    				Shader.TileMode.MIRROR);
    		paint2 = new Paint();
    
    		linearGradient3 = new LinearGradient(0, 0, 300, 0, new int[] { Color.RED, Color.YELLOW, Color.BLUE }, null,
    				Shader.TileMode.CLAMP);
    		paint3 = new Paint();
    
    		linearGradient4 = new LinearGradient(0, 0, 300, 300, new int[] { Color.RED, Color.YELLOW, Color.BLUE }, null,
    				Shader.TileMode.REPEAT);
    		paint4 = new Paint();
    
    		linearGradient5 = new LinearGradient(0, 300, 300, 0, new int[] { Color.RED, Color.YELLOW, Color.BLUE }, null,
    				Shader.TileMode.REPEAT);
    		paint5 = new Paint();
    	}
    
    	public LinearGradientView(Context context, AttributeSet attrs) {
    		super(context, attrs);
    	}
    
    	@Override
    	protected void onDraw(Canvas canvas) {
    		super.onDraw(canvas);
    
    		int left = 10, top = 20, right = 0, bottom = 0;
    		// 渲染到View的最右边
    		right = this.getWidth() - left;
    
    		// 渲染的每一个矩形高度，也可以简单理解为坐标系的结束值y
    		bottom = this.getHeight() / 5;
    
    		// 渲染器1
    		paint1.setShader(linearGradient1);
    		Rect rect1 = new Rect(left, top, right, bottom);
    		canvas.drawRect(rect1, paint1);
    
    		top = top + bottom;
    		// 渲染器2
    		paint2.setShader(linearGradient2);
    		Rect rect2 = new Rect(left, top, right, bottom * 2);
    		canvas.drawRect(rect2, paint2);
    
    		top = top + bottom;
    		// 渲染器3
    		paint3.setShader(linearGradient3);
    		Rect rect3 = new Rect(left, top, right, bottom * 3);
    		canvas.drawRect(rect3, paint3);
    
    		top = top + bottom;
    		// 渲染器4
    		paint4.setShader(linearGradient4);
    		Rect rect4 = new Rect(left, top, right, bottom * 4);
    		canvas.drawRect(rect4, paint4);
    
    		top = top + bottom;
    		// 渲染器5
    		paint5.setShader(linearGradient5);
    		Rect rect5 = new Rect(left, top, right, bottom * 5);
    		canvas.drawRect(rect5, paint5);
    	}
    }

简单期间，直接在Activity里面的setContentView里面加载：

package zhangphil.demo;
    
    import android.app.Activity;
    import android.os.Bundle;
    
    public class MainActivity extends Activity {
    
    	@Override
    	protected void onCreate(Bundle savedInstanceState) {
    		super.onCreate(savedInstanceState);
    		
    		LinearGradientView linearGradientView= new LinearGradientView(this); ;
    		setContentView(linearGradientView);
    	}
    }

代码运行结果：

![Center][]

[Center]: https://img-blog.csdn.net/20160723140724261?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center