Android Question How would you draw an arbitrary polygon FROM a sample image, as a square?

[NekoOtome]

I don't know how to put it into words very well, but imaging you want to copy from a sample texture to the screen
Instead of copying a square of the sample texture, you copy a polygon, I've connected the corners of how the output would be like
The reason is to fake a 2.5D effect the SNES/GBA are known for, particularly in racing games

 

[Brian Dean]

Have you seen this post from @Johan Schoeman - it is quite old but looks relevant. Try a search for "transformation" - there might be some more recent posts on this topic.

 

[NekoOtome]

That seems to be the other way around. From a square to a polygon.

 

[Brian Dean]

That seems to be the other way around. From a square to a polygon.

It makes no difference. A square is a polygon. You are simply (!) transforming one polygon into another polygon. The geometrical algebra which translates one coordinate pair into another coordinate pair does not know what a square is.

 

[Cableguy]

Maybe this

Thread 'OpenCV warp perspective' https://www.b4x.com/android/forum/threads/opencv-warp-perspective.167316/

 

[NekoOtome]

OpenCV seems to be it

Lib - Google Drive

drive.google.com

I recall libraries being 2 files, I've only been able to find an XML file. Have libraries in B4A been simplified since last I used it? Or do we have a way to download libraries from within B4A now?

 

[MasterGy]

Hi !

I quickly wrote a code module that draws a triangle from a 'bitmapcreator' texture into another 'bitmapcreator' object. You can draw a polygon with this, you just have to divide the polygon into triangles. It copies pixel by pixel, in principle it is fast, although I don't know what you want to use it for. It is good for drawing 2D triangles.

Sub DrawTriangle( _
BCsource As BitmapCreator,sx1 As Int,sy1 As Int, sx2 As Int,sy2 As Int, sx3 As Int,sy3 As Int, _
BCdest As BitmapCreator, dx1 As Int,dy1 As Int, dx2 As Int,dy2 As Int, dx3 As Int,dy3 As Int) As BitmapCreator

You specify a source, 3 coordinate points, a destination, and its 3 coordinate points.
It will draw the source onto the target and give you back a bitmapcreator, which is already the modified version.

 

[JordiCP]

OpenCV seems to be it

Lib - Google Drive

drive.google.com

I recall libraries being 2 files, I've only been able to find an XML file. Have libraries in B4A been simplified since last I used it? Or do we have a way to download libraries from within B4A now?

Please recheck the library link in the OpenCV thread.
Now it points to version 1.05 which is pretty much equal to 1.04 (by mistake I had removed the 1.04 .jar file from my Drive at some moment and it is no loger available).

 

[NekoOtome]

thank you.