Interest in supporting perspective division? #988
Description
Thank you very much for this package! And please forgive any misunderstandings I have; I'm not terribly familiar with the package internals.
I've found that for certain types of 3D diagrams, a perspective projection rather than an orthographic one sometimes conveys the idea more clearly. I've found this is particularly the case when dealing with round things, e.g.
#import "@preview/cetz:0.4.2": canvas, draw
#set page(width: auto, height: auto, margin: 0.6pt)
#let sph-to-cart(r, theta, phi) = (
x: r * calc.sin(theta) * calc.cos(phi),
y: r * calc.sin(theta) * calc.sin(phi),
z: r * calc.cos(theta)
)
#set text(size: 20pt)
#canvas(length: 6cm, {
import draw: *
circle((0,0,0), radius:0.0125, fill: black)
ortho(x: -60deg, y:0deg, z:-100deg, {
line((0,0,0), (1,0,0), stroke: red, mark: (end: "stealth"))
line((0,0,0), (0,1,0), stroke: green, mark: (end: "stealth"))
line((0,0,0), (0,0,1), stroke: blue, mark: (end: "stealth"))
content((1.1,0,0), $x$)
content((0,1.1,0), $y$)
content((0, 0, 1.1), $z$)
for phi in range(0, 360, step: 45) {
let points = ()
for theta in range(0, 181, step: 1) {
points.push(sph-to-cart(1, theta * calc.pi / 180, phi * calc.pi / 180))
}
line(..points, stroke: (paint: gray, thickness: 0.5pt))
}
for theta in (30, 60, 90, 120, 150) {
let points = ()
for phi in range(0, 361, step: 1) {
points.push(sph-to-cart(1, theta * calc.pi / 180, phi * calc.pi / 180))
}
line(..points, stroke: (paint: gray, thickness: 0.5pt))
}
})
})My understanding is that Cetz is already using homogeneous coordinates for everything internally, and indeed it's already possible to override the 4x4 view matrix. I think all that would be necessary to enable a true perspective projection instead of orthographic ones would be to add an option to do the final (x/w, y/w, z/w) perspective division step.
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