任意角度的渐变图片 Drawable

DegreeGradientDrawable.java

import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.drawable.Drawable;
import android.support.annotation.ColorInt;
import android.support.annotation.IntRange;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

public class DegreeGradientDrawable extends Drawable {
    @ColorInt
    private int[] gradientColors;
    private float[] positions;
    /**
     * from left to right, by clockwise. range 0 - 360.
     */
    private int degree;
    private float radius;

    private boolean isRectDirty;
    private RectF mRect = new RectF();
    private RectF mBoundRectF = new RectF();
    private final Paint mFillPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    private final Paint mStrokePaint = new Paint(Paint.ANTI_ALIAS_FLAG);

    public DegreeGradientDrawable(int degree, int[] colors, float[] positions) {
        this.degree = degree;
        this.gradientColors = colors;
        this.positions = positions;
        this.isRectDirty = true;
    }

    @Override
    public void draw(@NonNull Canvas canvas) {
        if (!ensureValidRect()) {
            return;
        }
        canvas.drawRoundRect(mRect, radius, radius, mFillPaint);
        canvas.drawRoundRect(mRect, radius, radius, mStrokePaint);
    }

    @Override
    public void setAlpha(@IntRange(from = 0, to = 255) int alpha) {

    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {

    }

    @Override
    public int getOpacity() {
        return 0;
    }

    public void setCornerRadius(float radius) {
        this.radius = radius;
    }

    public void setStroke(int width, @ColorInt int color) {
        setStrokeInternal(width, color);
        this.isRectDirty = true;
    }

    private void setStrokeInternal(int width, int color) {
        mStrokePaint.setStyle(Paint.Style.STROKE);
        mStrokePaint.setStrokeWidth(width);
        mStrokePaint.setColor(color);
    }

    @Override
    protected void onBoundsChange(Rect bounds) {
        isRectDirty = true;
    }

    private boolean ensureValidRect() {
        if (isRectDirty) {
            isRectDirty = false;

            Rect bounds = getBounds();
            float inset = mStrokePaint.getStrokeWidth() * 0.5f;

            mRect.set(bounds.left + inset, bounds.top + inset,
                    bounds.right - inset, bounds.bottom - inset);
            mBoundRectF.set(bounds);

            final float x0, x1, y0, y1;
            x0 = mRect.left;
            y0 = mRect.bottom;
            float _x1 = (float) (mRect.height() / Math.tan(Math.toRadians(degree)));
            float _y1 = (float) (mRect.width() * Math.tan(Math.toRadians(degree)));

            x1 = mRect.left + Math.max(mRect.right - mRect.left, _x1);
            y1 = mRect.bottom - Math.max(mRect.bottom - mRect.top, _y1);

            mFillPaint.setShader(new LinearGradient(x0, y0, x1, y1, gradientColors, positions, Shader.TileMode.CLAMP));
        }
        return !mRect.isEmpty();
    }
}