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-   -   linear transform in 2D screen space (https://forum.worldviz.com/showthread.php?t=2312)

 stefs 10-09-2009 06:36 AM

linear transform in 2D screen space

I intend to do some linear transform in 2D window (screen) space in order to do on-the-fly h-/v-keystone correction. I have all the code ready to calculate the linear distortion matrix from four registered corner points of the projection image. At the moment I choose this approach:

Code:

```current_pm = viz.MainWindow.getProjectionMatrix() current_pm.postMult(distortion_matrix) viz.MainWindow.setProjectionMatrix(current_pm)```
Where distortion_matrix is a 4x4 matrix that leaves the z untouched. The distortion in 2D space works fine but I still get some strange clipping artifacts.

My question: Is there a more elegant way in Vizard to implement this final viewport distortion as a 2D transform only rather than as a distortion of the 3D projection matrix?

 farshizzo 10-09-2009 10:15 AM

You can use a post-process shader to perform your keystone correction. A shader may be overkill for a simple linear transformation, but it allows for more flexibility for distortion correction. The vizlens module that comes with Vizard uses a post-process shader to perform the lens correction. Here is a simple example of a post-process shader:
Code:

```import viz import vizpp viz.go() KeystoneShader = """ uniform sampler2D vizpp_InputTex; uniform float osg_FrameTime; void main (void) {         float s = gl_TexCoord[0].s + (gl_TexCoord[0].t * sin(osg_FrameTime) * 0.3);         float t = gl_TexCoord[0].t;         gl_FragColor = texture2D( vizpp_InputTex, vec2(s,t) ); } """ vizpp.addEffect( vizpp.ShaderEffect(frag=KeystoneShader) ) viz.add('gallery.ive')```

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