Sparrow Forum

1. 

   MikeMania
   Member

   Hi,

   I've recently discovered the Sparrow Framework and have had a great time using it. However, part of my application involves painting with the touchscreen. The Demo TextureRender seemed great at first for this, but I am lost on how to correct the "flow" issue. As in, if the speed of my finger across the screen is too fast, the line would not be fully connected.

   Additionally, I have browsed the forum a bit and I am under the impression that the Sparrow Framework may not be the most suitable for this type of application?

   Thanks!

   Posted 10 months ago #
2. 

   Daniel
   Primary Feather

   Hi Mike,

   welcome to the Sparrow forum, and thanks for the compliments!

   To connect your paint strokes, you will have to manually draw other strokes between the current and the last touch position. SPTouch objects contain properties/methods to get the previous location of the finger; if the distance between the current and the previous position is too large, draw additional strokes between them. (You can calculate the positions manually, or you can use this method of SPPoint to help you.)

   If Sparrow is the correct library for your app depends on how complex your drawing requirements are! For simple drawings, it will be great, but if you need more control on the pixel-level, different blending functions, floodfill, etc., then you'll have to write some rendering (OpenGL) code manually, or use Core Graphics instead.

   Posted 10 months ago #
3. 

   MikeMania
   Member

   Thanks for the quick response. I've tried with the best of my ability, but there seems to be something missing. Here is my changes to the demo project. Where mConnect is a duplicate of mBrush used to draw the in-between.

   if (touch.phase == SPTouchPhaseEnded) continue;
    
           // find out location of touch event
           SPPoint *currentLocation = [touch locationInSpace:self];
           SPPoint *previousLocation = [touch previousLocationInSpace:self];
    
           mConnect.x = currentLocation.x + 0.5 * (previousLocation.x - currentLocation.x);
           mConnect.y = currentLocation.y + 0.5 * (previousLocation.y - currentLocation.y);
           [mRenderTexture drawObject:mConnect];
    
           // center brush over location
           mBrush.x = currentLocation.x - mBrush.width / 2.0f;
           mBrush.y = currentLocation.y - mBrush.height / 2.0f;
    
           // draw brush to render texture
    
           [mRenderTexture drawObject:mBrush];

   My direction also seems to break multitouch drawing.

   Forgive me, as this probably isn't as much an issue regarding Sparrow as it is about my inexperience with objective based programming.

   Posted 10 months ago #
4. 

   Durrza
   Member

   Hello Mike,
   linear interpolation formula is a*time + b*(1-time) or a bit more optimized a+(b-a)*time (with time going from 0 (returning a) to 1 (returning b). I am not sure what you want to achieve, but x+0.5(prevx-currentx) is not gonna work. If i read it right, you want to draw a brush from where the touch started to where the touch lifted. In that case you need to "save" the SPTouchPhaseStarted current x,y (and call them let's say startx, starty), and save the SPTouchPhaseEnded current x,y (and call them let's say endx, endy), then at the end of SPTouchPhaseEnded you need to draw a brush stroke from (startx,starty), to (end,endy). That should achieve what you wish to do.
   Cheers

   p.s. it's against my ever lasting love for sparrow to scare users away, but i think that the sparrow purpose is to create games, not drawing applications, which means that you are not going to find yourself very comfortable with it developing a drawing application.

   Posted 10 months ago #
5. 

   Dan
   Member

   We had some drawing code in Hairy Letters (the user could practice writing letters and it checks if they got it correct or not) we used a similar technique to this, just bear in mind that you'll likely need to do similar interpolation if the user moves their finger quickly. So this code should also be in SPTouchPhaseMoved with a check for whether the touch had moved significantly enough to warrant interpolation.

   Posted 10 months ago #
6. 

   Durrza
   Member

   Yes that is correct, during SPTouchPhaseMoved you need to store the "waypoints" of your interpolation!

   Posted 10 months ago #

RSS feed for this topic

Reply

You must log in to post.