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Change Custom View Canvas background color to transparent

I made a custom View Class that draws the waveform of an audio file, unfortunately, I'm having some problems with changing the background color of the canvas/custom view to transparent.
I can change the background color inside the onDraw function canvas.drawColor(Color.WHATEVER);
However, this works with any color but transparent, which shows black instead.
This works: canvas.drawColor(Color.BLUE);
This doesn't: canvas.drawColor(Color.TRANSPARENT);
Also, if I use the Android Studio Layout inspector, it seems to actually work, but in reality it does not. See the screenshot here:
Layout Inspector vs Android Emulator Screenshot
public class SimpleWaveform extends View {
Context context;
public Paint beforePlaySectionPencil = new Paint();
public Paint playSectionPencil = new Paint();
public Paint afterPlaySectionPencil = new Paint();
public Paint peakPencilBefore = new Paint();
public Paint peakPencilPlay = new Paint();
public Paint peakPencilAfter = new Paint();
public Paint xAxisPencil = new Paint();
public void init() {
beforePlaySectionPencil.setStrokeWidth(10);//set bar width (ERA /2)
beforePlaySectionPencil.setColor(ContextCompat.getColor(getContext(), R.color.aaDarkBlue));
playSectionPencil.setStrokeWidth(10); // (ERA /2)
playSectionPencil.setColor(ContextCompat.getColor(getContext(), R.color.aaLightBlue));
afterPlaySectionPencil.setStrokeWidth(10); // (ERA /2)
afterPlaySectionPencil.setColor(ContextCompat.getColor(getContext(), R.color.aaDarkBlue));
peakPencilBefore.setStrokeWidth(barGap / 8);//set peak outline width (ERA /6)
peakPencilBefore.setColor(0xfffe2f3f);
peakPencilPlay.setStrokeWidth(barGap / 8); //(ERA /6)
peakPencilPlay.setColor(0xfffe2f3f);
peakPencilAfter.setStrokeWidth(barGap / 8); //(ERA /6)
peakPencilAfter.setColor(0xfffe2f3f);
xAxisPencil.setStrokeWidth(1);
xAxisPencil.setColor(0x88ffffff);
#Override
protected void onDraw(Canvas canvas) {
if (clearScreenListener != null) {
clearScreenListener.clearScreen(canvas);
} else {
canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
}
if (clearScreen) {
clearScreen = false;
return;
}
drawWaveList(canvas);
canvas.drawColor(Color.TRANSPARENT);
}
private void drawWaveList(Canvas canvas) {
if (showBar) {
canvas.drawLines(barPoints, 0, playSectionLeftOffset * barUnitSize, beforePlaySectionPencil);
canvas.drawLines(barPoints, playSectionLeftOffset * barUnitSize, (playSectionRightOffset - playSectionLeftOffset) * barUnitSize, playSectionPencil);
canvas.drawLines(barPoints, playSectionRightOffset * barUnitSize, (barNum - playSectionRightOffset) * barUnitSize, afterPlaySectionPencil);
}
if(showXAxis){
canvas.drawLines(xAxisPoints, xAxisPencil);
}
}
}

I did a bit of research and found out how to achieve that in a canvas.
Take a look at this explanation.

Drawing rectangles that fill up with gradient depending on the value

I want to have three separate rectangles that would fill up with gradient. Depending on the value X the gradient would be placed differently. For example if value X = 75 the gradient would be 75% green and 25% red. I wanted to know if there is any library or a method that would allow me to do this in java (android studio).

To implement this, you could use LinearGradient for the gradient and then create a custom view with methods allowing you to change the layout of the gradient.
public class GradientView extends View {
Paint paint;
LinearGradient gradient;
int[] colors = [Color.RED, Color.GREEN];
public GradientView(Context context, int gradientHeight) {
super(context);
paint = new Paint();
setGradientHeight(gradientHeight);
}
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
paint.setShader(colorGradient);
canvas.drawPaint(paint);
}
public void setGradientHeight(int height){
colorGradient = new LinearGradient(0, 0, 0, height * 0.01 * super.getHeight(), colors, null, Shader.TileMode.MIRROR);
paint.setShader(colorGradient);
invalidate();
}
}
Haven't tested the code, but it should certainly work something like this.

Animate rotation of an image in Android

I have a gear image which I want to continuously rotate about a fixed point.
Earlier I was accomplishing this by including the image in my Android class as an ImageView and applying a RotateAnimation to it.
#InjectView(R.id.gear00) ImageView gear00;
RotateAnimation ra07 = new RotateAnimation(0, 359, 129, 186);
ra07.setDuration(10000);
ra07.setRepeatCount(RotateAnimation.INFINITE);
ra07.setInterpolator(new LinearInterpolator());
gear00.setAnimation(ra07);
Basically, I was injecting the ImageView into the class and applying a rotation animation.
However, I dont have the luxury of using an ImageView anymore. I have to use a Bitmap and rotate it on the canvas.
How can I go about accomplishing what I was doing earlier in the onDraw() method with a bitmap rotating about a fixed point continiously on the canvas?
Edit1:
I tried one of the suggestions mentioned below my code looks a little like the following
in onCreate():
Matrix matrix = new Matrix();
matrix.setRotate(10, 100, 200);
Then in onDraw() (where gear00Scaled is a bitmap to be rotated on the canvas):
canvas.drawBitmap(gear00Scaled, matrix, new Paint());
Another method I tried involved saving the canvas, rotating it, then restoring it:
canvas.save();
canvas.rotate(10);
canvas.drawBitmap(gear00Scaled, 100, 200, null);
canvas.restore();
Neither seem to be working though!

Make an XML class (suppose: rotate.xml) and place it in res/anim folder and then write the following code in it:
<?xml version="1.0" encoding="utf-8"?>
<rotate xmlns:android="http://schemas.android.com/apk/res/android"
android:fromDegrees="0"
android:interpolator="#android:anim/linear_interpolator"
android:pivotX="50%"
android:pivotY="50%"
android:repeatCount="infinite"
android:toDegrees="360" />
Then in your java class, do the following in OnCreate:
final Animation a = AnimationUtils.loadAnimation(CustomActivity.this,
R.anim.rotate);
a.setDuration(3000);
gear00.startAnimation(a);
OR
To do it using bitmap, I hope the following sequence of code helps you:
Bitmap targetBitmap = Bitmap.createBitmap(targetWidth, targetHeight, config);
Canvas canvas = new Canvas(targetBitmap);
Matrix matrix = new Matrix();
matrix.setRotate(mRotation,source.getWidth()/2,source.getHeight()/2);
canvas.drawBitmap(source, matrix, new Paint());
If you check the following method from:
~frameworks\base\graphics\java\android\graphics\Bitmap.java
public static Bitmap createBitmap(Bitmap source, int x, int y, int width, int height,
Matrix m, boolean filter)
this would explain what it does with rotation and translate.

I want to rotate a custom image as progress dialog in my application. You can use the code below to rotate an image:
RotateAnimation anim = new RotateAnimation(0.0f, 360.0f ,
Animation.RELATIVE_TO_SELF, .5f, Animation.RELATIVE_TO_SELF, .5f);
anim.setInterpolator(new LinearInterpolator());
anim.setRepeatCount(Animation.INFINITE);
anim.setDuration(1000);
imageView.setAnimation(anim);
imageView.startAnimation(anim);

In your onCreate() do
Matrix matrix = new Matrix();
And in onDraw
float angle = (float) (System.currentTimeMillis() % ROTATE_TIME_MILLIS)
/ ROTATE_TIME_MILLIS * 360;
matrix.reset();
matrix.postTranslate(-source.getWidth() / 2, -source.getHeight() / 2);
matrix.postRotate(angle);
matrix.postTranslate(centerX, centerY)
canvas.drawBitmap(source, matrix, null);
invalidate(); // Cause a re-draw
ROTATE_TIME_MILLIS is the full circle time, e.g. 2000 is 2 seconds.

Two things before the code:
You can't use imageview at all at all? Cause you could link it to a canvas and use a bitmap, but it is still an imageview.
I believe the main issue you are having is the other answer is not animating it and you are missing the call to invalidate() the view and redraw it as rotated.
So there are two approaches:
1st is with the imageview, personally I think it is easier and nicer. Below is a method in my activity class and mLittleChef is an ImageView.
public void doCanvas(){
//Create our resources
Bitmap bitmap = Bitmap.createBitmap(mLittleChef.getWidth(), mLittleChef.getHeight(), Bitmap.Config.ARGB_8888);
final Canvas canvas = new Canvas(bitmap);
final Bitmap chefBitmap = BitmapFactory.decodeResource(getResources(),R.drawable.dish_special);
//Link the canvas to our ImageView
mLittleChef.setImageBitmap(bitmap);
ValueAnimator animation= ValueAnimator.ofFloat(0, 359, 129, 186);
animation.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
#Override
public void onAnimationUpdate(ValueAnimator animation) {
float value = (Float) animation.getAnimatedValue();
//Clear the canvas
canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
canvas.save();
canvas.rotate(value, canvas.getWidth()/2, canvas.getHeight()/2);
canvas.drawBitmap(chefBitmap, 0, 0, null);
canvas.restore();
mLittleChef.invalidate();
}
});
animation.setInterpolator(new LinearInterpolator());
animation.setDuration(1000);
animation.start();
}
The other way to do it is with a custom canvas class. Instead of an ImageView, I create my own custom view class for ExampleDrawView mLittleChefDraw; in my layout. You will probably have to monkey with this one a bit to get exactly what you are looking for in terms of rotation, I made it just do a 360 degree turn using the middle of the canvas as the pivot point.
public class ExampleDrawView extends View {
Bitmap bitmap;
Float mRotate= 0f;
Handler h;
//State variables
final int STATE_PAUSE = 2;
final int STATE_ROTATE = 3;
int STATE_CURRENT;
public ExampleDrawView(Context context, AttributeSet attrs) {
super(context, attrs);
h = new Handler();
bitmap= BitmapFactory.decodeResource(getResources(), R.drawable.dish_special);
STATE_CURRENT= STATE_PAUSE;
}
Runnable move = new Runnable() {
#Override
public void run() {
switch (STATE_CURRENT){
case STATE_ROTATE:
if (mRotate<360){
mRotate++;
invalidate();
}else{
STATE_CURRENT= STATE_PAUSE;
}
h.postDelayed(move, 20);
break;
}
}
};
public void startDrawing(){
if(STATE_CURRENT == STATE_PAUSE){
STATE_CURRENT= STATE_ROTATE;
mRotate=(float) 0;
h.postDelayed(move, 20);
}
}
#Override
protected void onDraw(Canvas canvas){
super.onDraw(canvas);
//change your rotate point here, i just made it the middle of the canvas
canvas.rotate(mRotate,getWidth()/2,getHeight()/2);
canvas.drawBitmap(bitmap, 0, 0, null);
}
}
And then back in the activity call this to start it:
public void doCanvasCustomView(){
mLittleChefDraw.startDrawing();
}

Android draw circle with 2 colors (Pie chart)

This is my first question here at stackoverflow.com so excuse myself if i'm doing stuff wrong.
I want to create a circle which basically is like a progress bar. Now I'd like to set the percentage through some code.
What I want to achieve is: https://raw.github.com/psud/Melde-App/master/res/drawable-hdpi/circlemiddle.png
My problems:
Can't get a circle with two colors to work (have been searching forums for hours and have found solutions to problems similar to mine but I just can't implement those solutions that into my app. I've read a lot about canvas.drawArc(...) but can't seem to find out how to use it).
How is it possible to put a canvas into a layout? (I've got a xml layout and the canvas should be drawn inside a particular layout without changing the rest of the layout).
Thanks.

This is only a hint. It is simply a view that draw two arcs in the same rect: First arc spans from angle 0 to 360. The second one (above the first) spans from 0 to an angle that depends on the percentage.
public class PercentView extends View {
public PercentView (Context context) {
super(context);
init();
}
public PercentView (Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public PercentView (Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
paint = new Paint();
paint.setColor(getContext().getResources().getColor(R.color.lightblue));
paint.setAntiAlias(true);
paint.setStyle(Paint.Style.FILL);
bgpaint = new Paint();
bgpaint.setColor(getContext().getResources().getColor(R.color.darkblue));
bgpaint.setAntiAlias(true);
bgpaint.setStyle(Paint.Style.FILL);
rect = new RectF();
}
Paint paint;
Paint bgpaint;
RectF rect;
float percentage = 0;
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//draw background circle anyway
int left = 0;
int width = getWidth();
int top = 0;
rect.set(left, top, left+width, top + width);
canvas.drawArc(rect, -90, 360, true, bgpaint);
if(percentage!=0) {
canvas.drawArc(rect, -90, (360*percentage), true, paint);
}
}
public void setPercentage(float percentage) {
this.percentage = percentage / 100;
invalidate();
}
}
Add to your layout:
<bla.bla.PercentView
android:id="#+id/percentview"
android:layout_width="100dp"
android:layout_height="100dp" />

You can implement a pie chart quite easily with this library (achartengine - https://code.google.com/p/achartengine/) instead of rolling your own solution.

Android Custom Brush Colors

I'm trying to make custom brushes for my Android painting app. I started with Michael's code (found here) and I have managed to get .png brushes and use that as a bitmap and redraw it. It works fine but I can't change the colour. Tried using the setcolorfilter and colormatrixfilter but it doesn't seem to be working. Anyone knows how I can do this?
private Bitmap mBitmapBrush;
private Vector2 mBitmapBrushDimensions;
private List<Vector2> mPositions = new ArrayList<Vector2>(100);
private Paint mPanit;
public MyView(Context c) {
super(c);
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
mBitmapBrush = BitmapFactory.decodeResource(c.getResources(),R.drawable.brush1);
mBitmapBrushDimensions = new Vector2(mBitmapBrush.getWidth(), mBitmapBrush.getHeight());
}
#Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(0xFFAAAAAA);
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
for (Vector2 pos : mPositions) {
canvas.drawBitmap(mBitmapBrush, pos.a, pos.b, mPanit);
}
invalidate();
}
When I tried using the Colormatrixfilter, the .set function was giving an error.

I had the same issue. In order to change the bitmap color you need to add color to your paint object and apply it into bitmap. See the working example here,
for (Vector2 pos : customBrushMap.get(p)) {
Paint paint = new Paint();
ColorFilter filter = new PorterDuffColorFilter(R.Color.GREEN, PorterDuff.Mode.SRC_IN);
paint.setColorFilter(filter);
canvas.drawBitmap(mBitmapBrush, pos.x, pos.y, paint);
}
Result,