Valentin

I'm wondering what jitter function could be used to transform the shape of a quicktime movie - e.g. I want to playback a quicktime movie in a window.. but reshape it to a trapezoidal shape.

Is there a function that allows you to specify four corners for the output matrix or something like that - to easily reshape the video portion of the image? I don't mind if it still appears within the context of a rectangular output matrix.. but the quicktime video playing within that "box" needs to be shaped as a trapezoid (or rhombus or whatever i choose)

jitter-matrix-re-shapingtransform

I guess a good way to envision what I want is to give an example :

Lets say that I want to take a normal 4:3 or 16:9 quicktime movie, and project it so that it fits prefectly on a trapezoidal scrim.

(i.e. top and bottom parallel, but top maybe 2/3 or so the width of the bottom) I don't want to just crop or mask the image, i want to distort it in jitter to fit the trapezoidal shape of the surface.

I did look at mxform2d - but the docs don't give any useful examples of how to use it to achieve any particular transformation of the image.. I could try to dig into the math - but it would be great to know if there is a simple way to understand what that function really does :-)

On Dec 7, 2006, at 7:23 AM, Valentin wrote:

> (i.e. top and bottom parallel, but top maybe 2/3 or so the width of 

> the bottom) I don't want to just crop or mask the image, i want to 

> distort it in jitter to fit the trapezoidal shape of the surface.

On the CPU, you will probably want to use jit.expr->jit.repos to 

perform this operation since it isn't a 2D linear transformation (can 

sort of be done in 3D by rotating about the X axis with a projective).

Since this is just for output, however, I'd suggest you use OpenGL to 

do this on the GPU since it will be faster. You can draw a 

trapezoidal quad of your choosing with jit.gl.sketch and something 

like the following command list where you replace in the top/bottom/ 

Hope this gets you pointed in the right direction.

> (i.e. top and bottom parallel, but top maybe 2/3 or so the width of  
> the bottom) I don't want to just crop or mask the image, i want to  
> distort it in jitter to fit the trapezoidal shape of the surface.

On the CPU, you will probably want to use jit.expr->jit.repos to  
perform this operation since it isn't a 2D linear transformation (can  
sort of be done in 3D by rotating about the X axis with a projective).

Since this is just for output, however, I'd suggest you use OpenGL to  
do this on the GPU since it will be faster. You can draw a  
trapezoidal quad of your choosing with jit.gl.sketch and something  
like the following command list where you replace in the top/bottom/ 
left/right x/y values accordingly.

glbegin tri_strip
gltexcoord 0. 1.,
glvertex topleft_x topleft_y 0.,
gltexcoord 1. 1.,
glvertex topright_x topright_y 0.,
gltexcoord 0. 0.,
glvertex bottomleft_x bottomleft_y 0.,
gltexcoord 1. 0.,
glvertex bottomright_x bottomright_y 0.

Thank you so much - I will take a look shortly and get back to you :-)

This forum is just awesome... many helpful people :-)

Jitter Matrix re-shaping/transform?