Compositing Virtual Coordinate System

The virtual coordinate system uses a fixed height for all images and canvases of 8640 units. The virtual width of a canvas or image depends on its aspect ratio, making the virtual units as wide as they are tall. The point of origin of a canvas is in the center, and values increase toward the top and toward the right.
If the width of the canvas or image is an even number of pixels there is no exact center to a line, and the pixel at one half the width is considered the horizontal center, making the left half one pixel wider.
The same applies to the vertical dimension.

The value 8640 was chosen as the virtual height for a number of reasons:

  • It is a fairly large number, larger than any currently used formats.
  • It is an integer multiple of all the commercially used distribution formats:
    • 480 x 18
    • 576 x 15
    • 720 x 12
    • 1080 x 8
Using a virtual coordinate system with the origin in the center allows for moving projects from one format to another without the need to recompute coordinates. The only changes one might want to make would be to reposition some elements when changing from one aspect ratio to another.










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