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：
