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Android canvas not drawing

I have found very few tutorials on how to use the android canvas. However, after looking at the official documentation I was able to produce this code. I simply would like to draw a green rectangle.
public class LevelActivity extends AppCompatActivity {
Object shape;
Target target;
Rect r;
Paint paint;
Bitmap b = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(b);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_level);
paint = new Paint();
paint.setColor(Color.GREEN);
paint.setStyle(Paint.Style.FILL);
r = new Rect();
r.set(0,0,c.getWidth(),c.getHeight()/2);
c.drawRect(r,paint);
shape = new Shape(30,10); //Object setup
//shape.pick(); //Pick random point for target
}
}
I do not want to use a customView to draw, I just want to use pure android canvas. When I run the code I get no errors or any warnings.
Any help is greatly appreciated.
-Kelton

Well, you have a Canvas c with an underlying Bitmap b. Now anything that you draw on the Canvas c will actually be drawn on the Bitmap b. And you have done the drawing part in the above code. The Bitmap b has your drawn rectangle. But now to view that you need to load this Bitmap b in some view, like an ImageView. You can have an ImageView in your activity_level layout and then use ImageView.setImageBitmap(b) to load the Bitmap onto the view.

you need to add the following 2 lines at the end:
ImageView iv= (ImageView) findViewById(R.id.imageview_where_i_will_put_my_awesome_green_rectangle);
iv.setImageBitmap(b);

You have to create a ImageView and set the Bitmap as the one you created with canvas.
ImageView imageView = new ImageView(this);
imageView.setBitmap(bitmap);
addContentView(imageView, new LayoutParams(MATCH_PARENT, MATCH_PARENT));

Libgdx texture sizes, developing for bigger resolution than my laptop's

I'm currently working on a libgdx game and before I give it final touches I wanted to actually hear something from experienced users, that has been bothering me for a few days already.
If I want to support as many as possible devices, essentially I will be designing graphics for the biggest possible res ,which is then going to be scaled if needed, for smaller screens, right? How do I go about developing for a resolution that is even bigger than my laptop's(the 2015/16 gen phones). My laptop has a resolution of 1920x1080px and the S7 Samsung has 2k+ width.
Thank you!

I think what you are looking for is Viewports. You have to decide which strategy fits best your needs. For example a FitViewport always keeps the aspect ratio you define, which might lead to black bars on some devices.

When I personally develop with libgdx I place and size all objects relative to the screen width and height. This includes images, fonts, buttons, etc. This gives me a pretty consistent result across all devices because most devices today have a ratio 16:9 or something close to it. For developing an image larger than your screen size what's wrong with just using photoshop to create the image of the specified size?

Better you choose the screen with as 1280 and screen height as 800 and also use the fill viewPort . So you will be able to render your game in almost all the screens without the issue of stretching.
Viewport is the method which provided by the libgdx to solve this multi screen compatible issue . here i will post some sample code which you can use for the reference.
public class myGame extends ApplicationAdapter {
public OrthographicCamera camera;
public Viewport viewPort;
private SpriteBatch batch;
private BitmapFont myScoreFont;
private Texture texture;
public myGAme() {
}
#Override
public void create() {
myScoreFont = new BitmapFont(Gdx.files.internal(Constants.PATH_TO_MY_SCORE_FONT), true);
batch = new SpriteBatch();
float w = Gdx.graphics.getWidth();
float h = Gdx.graphics.getHeight();
texture = new Texture(Gdx.files.internal(Constants.PATH_TO_LEFT_BAR));
camera = new OrthographicCamera();
camera.position.set(0, 0, 0);
camera.update();
camera.setToOrtho(false, Constants.APP_WIDTH, Constants.APP_HEIGHT);
// Here is the viewport is setting up with the camera and the screen size
viewPort = new FillViewport(1280, 800, camera);
}
#Override
public void dispose() {
batch.dispose();
}
#Override
public void render() {
Gdx.gl.glClearColor(1, 1, 1, 1);
Gdx.gl.glClear(GL30.GL_COLOR_BUFFER_BIT);
float deltaTime = Gdx.graphics.getDeltaTime();
batch.setProjectionMatrix(camera.combined);
batch.begin();
batch.draw(myScorefont,"Score",0,0);
batch.end();
}
#Override
public void resize(int width, int height) {
// the game area will be resized as per the screen size of the device
viewPort.update(width, height);
}
#Override
public void pause() {
}
#Override
public void resume() {
}
}

Android Studio drawBitmap on a Canvas not working

I want to draw an image onto my canvas of my Android Application in Android Studio. The c.drawBitmap() function has an error.
It says: 'Cannot resolve method 'drawBitmap(android.graphics.Bitmap, int, int, int, int)'
Bitmap bg;
protected void onCreate(Bundle savedInstanceState) {
...
bg = BitmapFactory.decodeResource(getResources(), R.drawable.bg);
...
}
public void run() {
...
Canvas c = holder.lockCanvas();
c.drawBitmap(bg, 100, 100, 400, 200); // error occurs here
...
}
I am completely new to Android development and I could not find a solution.
Thanks.

Because you have the wrong parameters. You want either drawBitmap(Bitmap bitmap, float left, float top, Paint paint) or drawBitmap(Bitmap bitmap, Rect src, Rect dst, Paint paint)

Drawing WebView into set position on Canvas

I have created a custom WebView, which will be used to play a gif file. Now I need to draw this to my canvas in a specific position and using a set size.
However, I am not entirly sure how I can convert this webView containing Gif into a Bitmap so that I can insert it into the correct location on my Canvas.
My WebView Class:
public class finishWebView extends WebView
{
public finishWebView(Context context, String path)
{
super(context);
loadUrl(path);
}
}
Getting the raw resource for main Activity:
finishWebView view = new finishWebView(context, "file:///android_asset/test.gif");
The orginal code to convert my image to the correct size and insert into canvas:
finish = BitmapFactory.decodeResource(getResources(), R.drawable.finish);
finish = Bitmap.createScaledBitmap(finish, (PhoneWidth / 5), (PhoneWidth / 5), true);
protected void onDraw(Canvas canvas)
{
canvas.drawBitmap(finish, (j * totalCellWidth), (i * totalCellHeight), null);
}
So essentially, I need to work out a way to draw the webView with gif image displaying onto the specified locations within my canvas, similar to what I am currently doing with 'canvas.drawBitmap(...)'.
----------------------------------- EDIT ----------------------------------------
Using the code snippet mentioned provided by mikejonesguy, I have got to here, however this now just displays a blank screen.
public static Bitmap createBitmapFromView(View v) {
Bitmap b = Bitmap.createBitmap(100, 100, Bitmap.Config.RGB_565);
Canvas c = new Canvas(b);
v.draw(c);
return b;
}
// Within onDraw
GIFView gifView = new GIFView(context);
canvas.drawBitmap(createBitmapFromView(gifView), (j * totalCellWidth), (i * totalCellHeight), null);
I have tested my GIFView on normal xml layout pages and it works correctly, just cannot get it inserted into my canvas.

There are several ways to convert a view into a bitmap. This method is one way:
public static Bitmap createBitmapFromView(View v) {
Bitmap b = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.RGB_565);
Canvas c = new Canvas(b);
v.draw(c);
return b;
}
You'll have to wait until your webView has finished loading the GIF, of course, before you call this to get the bitmap.
If you're just trying to play an animated gif, this other SO post might help: Showing gif in android

How to overlay list item text color in specific region?

Let suppose we have the custom ListView which extends onDraw() method by drawing some rectangle in it.
class Listpicker extends ListView {
//..Some other methods here..//
#Override
protected void onDraw(android.graphics.Canvas canvas) {
super.onDraw(canvas);
canvas.drawBitmap(glassPickerBitmap, null, glassRect, semiTransparrentPaint);
}
}
The bitmap drawn represent some sort of glass which is rectangle with width equal to the width of listview and some height. What I want is when list item scrolls into this rectangle the color used for drawing text (not all item with background and etc.) would be changed into some another color. So, for example, when list item fits so that only half height of text fits into glassPickerBitmap, the outside part of list item should remain in its ordinal colors, and the part that is inside glassPickerBitmap should change its text color. List items are simple TextViews without any background.
How can be this achieved? Maybe any ColorFilters assigned to the Paint? But where? onDraw() method of Listview is not even called when ListView is scrolled... Can be this done inside customized views, for example, that will be ListView's items? Or may be some Color/Shader/do not know what else overlay can be used here, but where?
EDIT (added image examples):
Here is example of some crop from real-life app. There are 2 ListViews: one on the left side, other on the right. Glass is the grayed rectangle. Now, left list has "United States Dollar" currency selected. And I am scrolling right ListView in that way, that selection is somewhere between USD and Afghan Afghani. Now, what I want, is that USD currency in the left ListView would be drawn in red (exact color doesn't matter now, I will change it later to something meaningful) AND, in the same time, bottom part of "United States Dollar" and top part of "Afghan Afghani" in the right ListView would be drawn also in the same red color.
This color changing should be done in dynamic way - color should be changed only for the part of text that is under glass rectangle during scrolling of the list.
*OK, EUR and USD here are special currencies drawn with not standard cyan color. The question is about at least text with white color. But if it will be possible to change also cyan color it would be great.

As you can tell in their implementation they use and update a fixed position in their ListAdapter so then they update the View that matches accordingly, which is to me the easiest and simpler way to do it, but you don't get the half-half colored text, which I think you still want :)
So here is probably one of the worst answers I've given, sorry about it, I'll probably revisit this or hope someone can point you to a better solution
You can see a blurry demo at:
http://telly.com/Y98DS5
The dirty way:
Create a Paint with a proper ColorMatrixColorFilter, for the purposes of answering this I'm just desaturating, you'll have to figure out your 5x4 matrix for ColorMatrix to get the cyan your looking for. Also you will need some Rects to define source and dest when drawing below.
Create an off screen Bitmap and Canvas which you'll use to draw your list, that's done in onSizeChanged so we have proper view layout values, here you can start noticing the dirtiness as you will have to allocate a Bitmap as big as your ListView so you may get OutOfMemoryException.
Override draw to use your off screen Canvas and let ListView draw to it, then you can draw the Bitmap to the given Canvas that will draw your list as usual, then draw just the part of that Bitmap which will be drawn differently using the Paint we defined before, you will get overdraw for those pixels.
Finally draw your pre-fabricated glass Bitmap, I would recommend a n-patch (9-patch) so it scales and looks sharp across screens and densities, then you get more overdraw for those pixels.
The whole cake looks like:
public class OverlayView extends ListView {
private RectF mRect;
private Rect mSrcRect;
private Paint mPaint;
private Canvas mCanvas;
private Bitmap mBitmap;
private float mY;
private float mItemHeight;
public OverlayView(Context context) {
super(context);
initOverlay();
}
public OverlayView(Context context, AttributeSet attrs) {
super(context, attrs);
initOverlay();
}
public OverlayView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initOverlay();
}
private void initOverlay() {
// DO NOT DO THIS use attrs
final Resources res = getResources();
mY = res.getDimension(R.dimen.overlay_y);
mItemHeight = res.getDimension(R.dimen.item_height);
//
mRect = new RectF();
mSrcRect = new Rect();
mPaint = new Paint();
ColorMatrix colorMatrix = new ColorMatrix();
colorMatrix.setSaturation(0);
mPaint.setColorFilter( new ColorMatrixColorFilter(colorMatrix) );
}
#Override
public void draw(Canvas canvas) {
super.draw(mCanvas);
canvas.drawBitmap(mBitmap, 0, 0, null);
canvas.drawBitmap(mBitmap, mSrcRect, mRect, mPaint);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mRect.set(0, mY, w, mY + mItemHeight);
mRect.roundOut(mSrcRect);
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
}
}
So that said, I hope you end up with a cleaner solution, even if you don't get that half-half sexiness :)

First, keep a spare bitmap and canvas:
class Listpicker extends ListView {
Bitmap bitmapForOnDraw = null;
Canvas canvasForOnDraw = null;
Make sure it's the right size:
#override
protected void onSizeChanged (int w, int h, int oldw, int oldh) {
if (bitmapForOnDraw != null) bitmapForOnDraw.recycle();
bitmapForOnDraw = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
canvasForOnDraw = new Canvas(bitmapForOnDraw);
}
And when we come to drawing the list:
#override
protected void onDraw(android.graphics.Canvas realCanvas) {
// Put the list in place
super.onDraw(realCanvas);
// Now get the same again
canvasForOnDraw.drawColor(0x00000000, PorterDuff.Mode.CLEAR);
super.onDraw(canvasForOnDraw);
// But now change the colour of the white text
canvasForOnDraw.drawColor(0xffff00ff, PorterDuff.Mode.MULTIPLY);
// Copy the different colour text into the right place
canvas.drawBitmap(bitmapForOnDraw, glassRect, glassRect overwritePaint);
// finally, put the box on.
canvas.drawBitmap(glassPickerBitmap, null, glassRect, semiTransparrentPaint);
}