如何防止我的自定义视图绘图被视图边界剪裁？

Question

I'm attempting to extend ImageView and add a shadow. I'm running into a problem where the shadow is being clipped by the view bounds and looks quite bad:

I've attempted to set the width/height via LayoutParams programmatically as well as trying different XML properties like android:adjustViewBounds , but there is no change in the display. Similarly, setting a android:layout_margin is ineffective in preventing the shadow from being clipped.

Can anyone help me figure out how to avoid this clipping? I'm sure there is something obvious I'm overlooking here.

Update:

My code is very specific at this time to exactly one case: I'm trying to draw a circle "shadow" underneath a circle bitmap. It is obvious that the view bounds are causing the clipping, but I have not been able to find a solution that will allow me to expand the view bounds.

It has been claimed on #android-dev that my math is simply wrong. I am accounting for screen density, which is a common problem. I have triple checked my math on all counts and cannot find where it might be wrong.

Initially, on an xxhdpi screen, density 3.0, the 56dp image is exactly 168px wide and 168px high. After adding 2dp to the width and height to account for the offset, the layoutParams have width=174 and height=174.

My basic approach is to let the super ImageView do its thing and draw the bitmap specified in xml and all I want to do is draw a little something additionally. Is this approach fundamentally flawed?

I use the largest of width or height in onLayout to determine what the radius of my shadow circle should be: radius = Max(width, height) / 2. I draw a circle with this radius and center point at (Cx, Cy) where Cx is the midpoint of the width plus a x-offset and Cy is the midpoint of the height plus a y-offset to create the shadow effect. I draw the additional circle using a canvas to a bitmap and later in onDraw I place my circle on the canvas before allowing the ImageView super onDraw to take care of the source bitmap.

Additionally, in my onLayout I attempt to account for the x- and y-offset distances and add those to my view's width and height via LayoutParams , but no change in the size of the view is evidenced when the view is drawn.

Here is the code that I'm using: https://gitlab.com/dm78/ImageViewWithShadowExample/

Here is the relevant code:

activity_main.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
                xmlns:tools="http://schemas.android.com/tools"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                tools:context=".MainActivity">

    <dm78.example.imageviewwithshadowexample.CustomShadowImageView
        android:id="@+id/circle"
        android:layout_gravity="center"
        android:src="@drawable/circle"
        android:layout_margin="16dp"
        android:layout_width="56dp"
        android:layout_height="56dp"/>

</FrameLayout>

CustomShadowImageView.java

package dm78.example.imageviewwithshadowexample;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Build;
import android.renderscript.Allocation;
import android.renderscript.Element;
import android.renderscript.RenderScript;
import android.renderscript.ScriptIntrinsicBlur;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.util.TypedValue;
import android.widget.FrameLayout;
import android.widget.ImageView;

public class CustomShadowImageView extends ImageView {

    public static final String TAG = CustomShadowImageView.class.getSimpleName();
    public static final float SHADOW_RADIUS_DP = 3f;
    public static final float SHADOW_X_OFFSET_DP = 2f;
    public static final float SHADOW_Y_OFFSET_DP = 2f;

    private Paint mPaint;
    private float mShadowRadius;
    private float radius;
    private float cx;
    private float cy;
    private float mShadowXOffset;
    private float mShadowYOffset;
    private Bitmap mShadowBitmap;
    private FrameLayout.LayoutParams layoutParams;
    private boolean expanded;

    public CustomShadowImageView(Context context) {
        super(context);
        init();
    }

    public CustomShadowImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public CustomShadowImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        Log.d(TAG, "init " + this.hashCode());

        DisplayMetrics dm = getContext().getResources().getDisplayMetrics();
        mShadowRadius = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, SHADOW_RADIUS_DP, dm);
        mShadowXOffset = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, SHADOW_X_OFFSET_DP, dm);
        mShadowYOffset = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, SHADOW_Y_OFFSET_DP, dm);

        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        //noinspection deprecation
        int shadowColor = getContext().getResources().getColor(R.color.shadow);
        mPaint.setColor(shadowColor);

        expanded = false;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        Log.d(TAG, String.format("onMeasure %d w: %d, h: %d", this.hashCode(), MeasureSpec.getSize(widthMeasureSpec), MeasureSpec.getSize(heightMeasureSpec)));
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        Log.d(TAG, String.format("onLayout %d changed: %b, l: %d, t: %d, r: %d, b: %d", this.hashCode(), changed, left, top, right, bottom));
        super.onLayout(changed, left, top, right, bottom);

        if (changed) {
            if (!expanded) {
                layoutParams = (FrameLayout.LayoutParams) getLayoutParams();
                layoutParams.width = (int) (layoutParams.width + mShadowXOffset);
                layoutParams.height = (int) (layoutParams.height + mShadowYOffset);
                expanded = true;
            }

            cx = (right - left) / 2 + mShadowXOffset;
            cy = (bottom - top) / 2 + mShadowYOffset;

            boolean widthGreater = (right - left) > (bottom - top);
            radius = (widthGreater ? right - left : bottom - top) / 2;

            if (mShadowBitmap == null) {
                Bitmap bitmap = Bitmap.createBitmap(right - left, bottom - top, Bitmap.Config.ARGB_8888);
                Canvas canvas = new Canvas(bitmap);
                canvas.drawCircle(cx, cy, radius, mPaint);

                if (Build.VERSION.SDK_INT >= 17 && !isInEditMode()) {
                    RenderScript rs = RenderScript.create(getContext());
                    Allocation input = Allocation.createFromBitmap(rs, bitmap, Allocation.MipmapControl.MIPMAP_NONE, Allocation.USAGE_SCRIPT);
                    Allocation output = Allocation.createTyped(rs, input.getType());
                    ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
                    script.setRadius(mShadowRadius);
                    script.setInput(input);
                    script.forEach(output);
                    output.copyTo(bitmap);
                }

                mShadowBitmap = bitmap;
            }
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        Log.d(TAG, "onDraw " + this.hashCode());
        canvas.drawBitmap(mShadowBitmap, mShadowXOffset, mShadowYOffset, null);
        super.onDraw(canvas);
    }
}

Answer 1

By default, Views are only allowed by their parent to draw within their bounds and not beyond.

You have two options:

• Either you add some padding to your Imageview to enlarge its bounds instead of using layout_margin and you draw within these bounds.
• Either you disable the child clipping behavior by setting android:clipChildren="false" to your FrameLayout .

Answer 2

如果原因是视图父级的填充，则将以下行添加到父级 xml 元素：

android:clipToPadding="false"

Answer 3

android:clipChildren="false"在父布局中为我工作