Problem background
(Described in a tutorial here: https://github.com/mattdesl/lwjgl-basics/wiki/ShaderLesson3)
Heres is a circle displayed with a fragment shader.
Because of x,y coordinates with the range 0-1, the circle becomes an oval when the display object isnt a square.
In this case when width > height you can multiply the texCoord.x with some aspect ratio value (resolution.x/resolution.y) to get a round circle as a result:
Corona
In corona we have the provided uniforms CoronaContentScale and CoronaTexelSize. Initially I thought those uniforms could be used to calculate the aspect and or resolution but I just cant get it right.
Right now I ended up sending this information with the vertex userdata occupying 1/4 values since the uniform userdata is a forthcoming feature.
Please help me understand and solve this problem. Thank you
CoronaTexelSize , as its name suggests, will tell you only about the current texture (or the first one, in the case of composite effects), which is probably a small all-white rectangle for stock display objects like circles.
If you’re just getting started with this, one way to go about it would be hard-wire any constants into the shader, so for instance:
local Constants = ([[P\_UV float scale = %f;]]):format(display.contentWidth / display.contentHeight) kernel.fragment = Constants .. [[// REST OF YOUR SHADER HERE, use 'scale' somehow]]
If you don’t need much resolution you could also sneak that scale factor through a color channel (setFillColor() and then use CoronaColorScale() to recover it), though obviously you’d have to take more care if you still want some color!
A few other solutions are possible, but are probably a bit too involved at this stage.
CoronaTexelSize , as its name suggests, will tell you only about the current texture (or the first one, in the case of composite effects), which is probably a small all-white rectangle for stock display objects like circles.
If you’re just getting started with this, one way to go about it would be hard-wire any constants into the shader, so for instance:
local Constants = ([[P\_UV float scale = %f;]]):format(display.contentWidth / display.contentHeight) kernel.fragment = Constants .. [[// REST OF YOUR SHADER HERE, use 'scale' somehow]]
If you don’t need much resolution you could also sneak that scale factor through a color channel (setFillColor() and then use CoronaColorScale() to recover it), though obviously you’d have to take more care if you still want some color!
A few other solutions are possible, but are probably a bit too involved at this stage.