Render water-paint in iOS

Question

I have been working with OpenGL in iOS, and setting the colors with glColor4f(r,g,b,a) and then drawing my own color on a white UIImageView

Answer 1

If you are still struggling with the basics of getting realistic looking water colors working, you may want to experiment/prototype in photoshop first.

http://www.zoepiel.com/tutorials/watercolor/ shows some very effective tricks for creating watercolor images with simple tools.

The most interesting one is to multiply a group of watercolor layers with a greyscale watercolor paper image. The texture of the paper makes some parts remain white, and other parts saturate with color, just like real watercolor.

Each layer remains 'wet' in the sense that the colors within it blend, but the layers are 'dry' with respect to each other.

She also explains some of her brush and blur settings and shows what they do.

Once you can produce the desired effect in photoshop, you'll have clear specifications of what you want to do and you'll be quite a bit closer to programming it out.

Answer 2

Looking at the examples you posted, it looks like they are using a simple Gaussian Blur with a radius of double your brush size. This may be an incomplete solution, but it's at least the first level.