iOS Scaling method

[diehard89]

Is there any method to scale just the bottom half of an image, such as functions,etc...

For example, a square with width 10 and height 10.
After scaling, the top width of the square remains 10,but the bottom width is 5.(Height remain the same)

Thanks in advance.

 

[robbieduncan]

You don't really mean scaling do you? You mean to transform the image so it looks like it has perspective (so that the image is projected onto a trapezoid).

I think you can perform this transform using CoreGraphics calls although I am unable to provide details as I'm not on a Mac right now. Perhaps if you read the documentation you can work it out for yourself?

 

[diehard89]

ya,some kind of transformation, I will see if i can find it in the documentation.

 

[robbieduncan]

Hmm, looking at the documentation CoreGraphics only seems to have affine transformations. You need a non-affine transform. Perhaps you need to be looking at OpenGL?

 

[diehard89]

been looking in opengl ES but did not find much info on how to do it.

 

[diehard89]

In openGL, i bind the textures onto a quad made of GL_TRIANGLE_STRIP

but if i move in the bottom vertex of the Quad that made up of Triangle strip,
the texture that bind onto it will be distorted and not properly render.