But there are other easily adaptable algorithms, for example a texture generation effect that computes the value of each pixel based solely on its position. Many algorithms require some sort of coordinate transformation using matrices to set up a transformation, for example.
If an effect already has coordinate transformation machinery in its pipeline, there’s an alternative that’s often simpler. Using pixel coordinates to represent the particle positions seems fine (as long as the particles don’t have to rotate around a point), but when you go to actually render the particle textures, you’ll have to scale them by pixel aspect ratio and downsample factor. Suppose you’re writing a particle system effect that sprays textured sprites from a source position defined by an effect control point. Staying in the input coordinate space is an option, though you must account for pixel aspect ratio and downsample factor elsewhere. Any effect that colors pixels based solely on a linear function of the x and y coordinates need not bother with pixel aspect ratio and downsample factor at all. This means that any slider which defines a size in pixels will be a problem when the image is rendered downsampled the width of anti-aliasing filters changes based on downsample factor. Second, even if it is a square coordinate system, it’s not necessarily the same size as the final output. The distance between two points varies based on their angle in this coordinate system anything rotated in this system is skewed, in the final output. Circles will appear as ellipses, squares as rectangles. The final rendered image can be stretched or squashed horizontally, relative to the pixels your effect processes. But effects that use absolute pixel measurements or geometry must take a deeper look at the relationship between the input buffer and the final rendered image.ĭon’t Assume Pixels Are Square, Or 1-To-1 ¶įirst, it is not necessarily a square coordinate system, due to both pixel aspect ratio and non-uniform downsample factor. This provides an implicit “pixel coordinate system.” This coordinate system is handy and easy to understand. Point parameters are given to the effect scaled for downsample factor and pixel aspect ratio they are in the coordinate system of the input buffer. Simple effects needn’t do any work to match up point parameters to the actual pixels in the output. Even different layer parameters can have different pixel aspect ratios! Doing so isn’t difficult once you understand the concepts involved.
Don’t Assume Pixels Are Square, Or 1-To-1.Accessing the After Effects Function Suites.Compatibility Across Multiple Versions?.
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