Projection distortion

Projector distortion editing

Bend the rules.

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Racer can be used to project onto curved surfaces. For this purpose, you need Cg support (most graphics cards will support this). You won't normally use this on stand-alone Racer installations; it is only available for licensed users.

Racer uses a distortion texture to be able to map each pixel to a new location. This distortion texture is generated using a spline-based grid of 5x5 control points. Dragging each control point will modify the pixels in its surrounding. Therefore, this method can easily handle a lot of surfaces without needing to do too much work to match up the projector signals. However, for perfectly spherical surfaces, this method may be less than perfect.

Distortion normally works in sync with edge blending; that part deals with overlapping multiple projectors and smooth transitions from one projector to the next. Light isn't linear, so it's more tricky than just a linear blend.

To begin distortion editing, setup your installation as follows:

Set renderer.motion_blur.method to 4. FBO's are needed to handle distortion.
Set renderer.motion_blur.distorter.enable to 1. This enables the creation of a pixel mapping texture which is used in the post-processing phase to distort the image.
Set renderer.motion_blur.fs_filter1 to one of the distortion Cg shaders. See below for a list and explanation. For example: bloom_distort_edge_l_f.cg. This is needed to perform distortion and edge blending.

Distortion shaders are located in data/renderer/fullscreen_shaders_hdr and are the following:

bloom_distort_edge_l_f.cg; used for a multiview screen with edge blending on the left. So this is used for the right computer (racer_r.ini mostly).
bloom_distort_edge_r_f.cg; used for a multiview screen with edge blending on the right. So this is used for the left computer (racer_l.ini mostly).
bloom_distort_edge_lr_f.cg; used for a multiview screen with edge blending on the left. So this is used for the center computer (master).
bloom_distort_edge_none_f.cg; distortion without edge blending. Only useful for testing.

Distortion is controlled in racer.ini.

Parameter	Description
renderer.motion_blur.distorter.enable	Enable distortion (generates distortion texture upon program start, which is used by the fullscreen shaders described above)
renderer.motion_blur.distorter.auto_edit	Enter edit mode at startup? (v0.8.5+) (0=no, 1=yes)
renderer.motion_blur.distorter.init_testpattern	Initial test pattern; 0=none, 1=colored grid, 2=crosshairs
renderer.motion_blur.distorter.points_alpha	Alpha value of control points. Normally 1.0, but these may be set lower when used to drive with the crosshairs on (also set auto_edit to 1 in that case).
renderer.motion_blur.distorter.texture_size	Size of the distortion texture. Normally, use 1024. This may need to change as you change resolutions.
renderer.motion_blur.distorter.control_point_<xy>	2D coordinate of the control points (5x5 grid, so 25 in total). These are normalized values, ranging from around 0..1. Some control points will be outside of the view, so can have values slightly outside the 0..1 range. Normally these values are written during distorter edit sessions (the console command 'distort edit'), and not filled in by a user.

To enter distortion mode, enter the script command 'distort edit'.

Control (key)	Description
[, ]	Select control points. The selected point will be highlighted in white.
Left/right/up/down	Move control point (it's possible and needed to move some control points offscreen, so using the mouse to point & drag will not work for the outermost grid points).
Space	Toggle test patterns; none, colored grid and crosshairs. The crosshairs are useful to detect movements while enabling driving (the colored grid is too obvious so driving while it's enabled isn't possible). To enable the crosshair pattern at program start, set renderer.motion_blur.distorter.auto_edit to 1 and renderer.motion_blur.distorter.init_testpattern to 2. Furthermore, set renderer.motion_blur.distorter.points_alpha to 0 or a value near 0 (to hide the control points).
Ctrl-Up/Ctrl-Down	Modifies test pattern alpha (transparency)
R	Reset control points (covering the entire screen)
Ctrl-S	Save settings. This saves the control point locations in racer.ini.
ESC/ENTER	Stop editing
PageUp/PageDown	Modify control point alpha (transparency)
Mouse wheel	Edit gamma value. Normally, use a value around 2, which seems to work best.
Control key+mouse wheel	Edit edge blend 'p' value. That values is used in the edge blend curve. Normally best left at 1.

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(last updated November 13, 2012 )