Hi I am new to Android Canvas. I want to know how can I draw on canvas using a bitmap.
Basically I want to be able to draw multiple figures in my canvas dynamically. After reading about canvas I figured out this much that for each figure I may have to create a new bitmap attach a canvas to it draw a figure in that bitmap and finally draw that bitmap in the canvas of onDraw() method using drawBitmap function in order to view it on screen. Hope I am right till this part ? If not please correct me. I am open for your opinions and suggestions :)
Also I would like to know if I can apply onTouch event separately to the bitmaps or canvas created dynamically or it can be only applied to canvas of onDraw cause I want the images which are being drawn in my canvas to be able to move at users will?
You are right about the first part. However in second part u cannot add onTouch listener as u have said. As far as I know listeners can only be added to Views. And also its not like you are adding onTouch Listener to the canvas of the onDraw() method u are basically applying to the whole view a view cannot have two same listeners.
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I don't know alot about graphics and drawings but I am trying to do something on canvas, and that is using vector graphics instead of bitmap to draw path on canvas with finger , I cant find any documentation or tutorials to understand how to do that, but I know that this implementation is used by some drawing apps.
According to my searching I deduced that using vector graphics will never show pixels on the edges of the path even if you zoomed.
Please suggest any thing that might help me use vector graphics and attach it to canvas to draw, thanks.
If you just want to draw with the finger :
Assuming you have a custom View that covers the drawing area ...
On onTouch handler on ACTION_DOWN create a new Path object with origin at touch point, on ACTION_MOVE you add new segments to the Path and call invalidate().
On onDraw you draw the Path on the Canvas.
I'm writing a app for a tablet. I have a activity that contains text and buttons and an area where I want to put something that is drawn on a canvas. When buttons are pressed I want to draw a grid that will contain lines, text and images, built dynamically.
What I can't figure out is after I draw this on the canvas how to put/embed the canvas into the activity in a certain area(ImageView?). I have a prototype app where I can draw the grid, but I can't figure out how to put the canvas into the activity.
Any help or point me to an article would be really appreciated. Thanks
First you get a bitmap from your canvas then you can use it in your ImageView via ImageView.setImageBitmap(mCanvasBitmap)
I would like to display several rings with different coloured sections (see below). The colour of the sections, however, cannot be know in advance, so I will need to draw these dynamically.
I know I could draw directly to the canvas but, once I have them, I would like to animate these rings, rotate them, have them overlap etc. It seemed, therefore, that the easiest and possibly least expensive approach would be to create them in advance, in memory, as transparent pngs and then just draw them in onDraw.
My problem is the only methods I can find to do this are setPixel. Is there not a way I could use drawing tools, like in Canvas, to draw to an empty bitmap, once, then use that bitmap with my canvas in onDraw?
I feel like I am missing a piece in the puzzle. Any help would be greatly appreciated.
You can create a Bitmap that is the size you want the ring to be and then create a Canvas the same size. Call setBitmap() on the Canvas and it will draw on to that for you. Then you can build your circle and have a bitmap to hold onto and use just like any other resource.
I am extending the ImageView to display the images. The input stream for images is getting from socket along with their top left coordinates.
I am able to display the part of image,where as the remaining screen is white.My problem is total canvas is overridden with the current bitmap and the previous drawings are erased with white screen.
I searched for the solution,I come across to known the information about canvas is "Every pixel of canvas is drawn when canvas.drawBitmap(bitmap,top,left,paint) is called".
I need to update the only dirty part of image(canvas) without updating the entire canvas.
Please suggest me How to update the dirty part of screen(canvas) and previous drawings should not be erased.
Thanks & Regards
Mini.
You can make a canvas from what you already have instead creating a blank on and then draw on it. This is an example of how to achieve it.
yourImageView.setDrawingCacheEnabled(true);
Bitmap bm = yourImageView.getDrawingCache();
final Canvas canvas = new Canvas(bm);
Then you have a canvas, which contains whatever was previously in ImageView and you can update whatever part you want. For that I would recommend having a look at PorterDuff modes.
I am working on application in which i am drawing a image on the canvas now i want o draw the second image in that canvas.
for example see the image ......
the first image s looking as follow ....
when i click on some place then it will show as follow
but the other thing which is shown in the image (thymin) it should display as fadein in the canvas
how to do it i am not getting any thing can any one help me .....
That's quite complicated by the sounds of it though not impossible to achieve. I think it would take more than the standard View class to achieve this, more like you would need to use the SurfaceView class where you have greater control over what gets drawn and where and when. If you're not familiar with Android 2D graphics then a good place to start would be here.
For drawing the bitmap, you could use canvasObject.drawBitmap() method of Canvas class. drawBitmap takes a paint object as one of its parameters, you could programmatically vary the alpha value of the paint object to create a fade-in effect. Paint class has a setAlpha(value) method to do this. I haven't tried this out myself but this should work.