ericsinger

I'm trying to put a small matrix (320x240) in the center of a large one (640x480) and use the alpha channel of the smaller one to fade it in (from 0. to 1. transparency). To do this, I'm sending the large one into a [[jit.matrix 4 char 640 480 @dstdimstart 160 120 @dstdimend 480 360]], with [usedstdim 0] and [thru 0], then, the second one with [usedstdim 1] and [thru 1].

When I ramp the alpha down to zero by multiplying it by a 1.->0. float using [[jit.op @op * pass pass pass]], I would expect it to fade out. However, I'm getting a black box, as if jit.matrix is ignoring the alpha channel. I've tried jit.alphablend with no results, but I'm probably using it wrong. Ideas?

When I  ramp the alpha down to zero by multiplying it by a 1.->0. float using [[jit.op @op * pass pass pass]], I would expect it to fade out. However, I'm getting a black box, as if jit.matrix is ignoring the alpha channel. I've tried jit.alphablend with no results, but I'm probably using it wrong. Ideas?


picture-in-picture-alpha-blend

hard to say without seeing the patch, but strongly recommend you use opengl for this. 1 jit.world and 2 jit.gl.videoplanes are all that's needed.

http://music.arts.uci.edu/dobrian/Music215/S13/examples.htm#Ex38

For the old-school jit.alphablend method, see 

http://music.arts.uci.edu/dobrian/IAP2006/examples.htm

 and scroll down to the examples called "make a mask image" and "mask by alphablend".

To wit: http://music.arts.uci.edu/dobrian/Music215/S13/examples.htm#Ex38

For the old-school jit.alphablend method, see http://music.arts.uci.edu/dobrian/IAP2006/examples.htm and scroll down to the examples called "make a mask image" and "mask by alphablend".


here is a patch doing what you ask for , hope you learn from it :-)

"Picture in picture" alpha blend