2025-03-12

Last modified: 2025-03-12 17:58:11

• 2d polygon SDF
• Sketch editor
• Sketch pad/revolve
• Domain repetition
• Isoform todo

2d polygon SDF

I am having trouble getting the 2d polygon SDF to work.

It's meant to be a triangle, currently I'm not seeing anything at all.

OK, finally! I stopped doing ray marching and just plotted the immediate SDF value, and eventually made this work:

So now I'm happy that the 2d SDF is working, I can turn it 3d?

• the time taken to compile the shader is counted against the frame rendering time - we should only start counting after the shader is compiled

Here we go!

Working. Good.

And arc segments?

Arc segments not working. I don't quite understand the arguments to Quilez's arc segment function:

vec2 sdSqArc( in vec2 p, in vec2 a, in vec2 b, in float h, float d2min )

Skip it for now. So next up would be a polygon editor, but I want to fix the adaptive quality thing first.

OK, I got Cursor to make it rescale the render resolution without changing the canvas size. Seems to be working better.

• still doesn't know that it doesn't need to render while you're focused away

Nothing else to do: polygon editor time!

Sketch editor

I want to be able to edit the polygons in a SketchNode. I'm thinking that when we are editing a polygon we'll draw the scene with the ray marching fragment shader like normal, and then on top of that we'll have a layer where you can see the polygons that you're editing, in the same coordinate system as the object. Should the layer on top be drawn by another shader, or just with a second HTML canvas with a see-through background?

Features for a first pass:

• the SketchEditor class or whatever should take a SketchNode as an argument and only allow editing the first polygon in the node; and only allow line segments
• we pop up a sketch editing toolbar to put buttons in, including "split line segment", "delete vertex", "select/drag vertices", "no tool"
• when we have a SketchNode object selected in the tree we open up the SketchEditor
• while SketchEditor is open and one of the tools is selected, clicking and dragging no longer rotates the view
• draw the line segments of the polygon, and shade the interior in a slightly opaque colour to distinguish it from the exterior
• draw vertices with a circle that is a bit bigger than the line width, and a different colour

Alright!

Issues are:

• the coordinate system doesn't map correctly on anything but exactly looking at the XY plane
• can't change pan/zoom/rotate while in sketch editor

Fixing the coordinate system mapping is proving difficult. I've had a lot of attempts with claude-3.7-sonnet-thinking and still not got it. I'm trying o1 now. If o1 can't do it I may have to work it out myself.

The shader basically implements screenToWorld() - so maybe the thing to do is get that to work, and then get Cursor to write me the inverse?

OK, one key point is that the point comes into worldToScreen() with no Z coordinate, so we need to implicitly set Z=0.

Woo, working!

Now the issue is that screenToWorld() doesn't work properly. Needs to give an answer that has Z=0.

I have a workable version. It's not exactly right, but the error is small enough to live with for now. So, onwards.

Sketch pad/revolve

So now we need pad/revolve operations.

How should this interact with child elements that aren't sketches?

1. you can only do it on sketches
2. it evaluates its child element with z=0, so would act on a cross section
3. it just stretches out the middle of the plane and otherwise evaluates child as normal; so sketches become 0.01mm too long

I've gone with number 3 for now.

This is kind of working:

I have an extruded sketch (yay!), but the edges aren't being detected, which suggests the SDF is wrong.

• can we make infinite lattice functions that we can intersect with the shape to give the shape a latticed surface?

Also if I apply a "Roughen" to the extruded shape, it is obvious that it is a broken SDF, because I don't get the same pattern that I get on good SDFs.

I have Extrude kind of working now, but the Roughen looks like this:

That should be the same texture on the prism as on the box.

• we could make some of the object parameters into Uniforms so that we don't have to recompile the shader every time you change them, and these ones could allow interactive modifying with the mouse

OK, I am realising the problem. If I make my SketchNode render as a flat object, then its distance everywhere is basically 0, which is why it gives a broken shape when elongated. But if I make SketchNode ignore the Z coordinate then it renders as an infinite extrusion. I think "Extrude" and "Elongate" need to be separate operations. I also think "Elongate" may produce a broken SDF on the interior, unsure.

I need to make a TreeNode be able to declare that it is a 2d SDF, and I also need to be able to generate child shader code in 2d mode and 3d mode.

• 3d sketch in 3d mode: fine
• 2d sketch in 2d mode: fine
• 2d sketch in 3d mode: truncate at Z height of 0.01mm
• 3d sketch in 2d mode: slice at Z=0

Hmm, if I Transform a Sketch, I get a broken SDF again. Oh! It's because the Transform is evaluating the sketch's 3d shader code instead of its 2d shader code.

I guess for now we just make the Transform node check whether its child is a 2d SDF and evaluate its 2d code if so?

Oh no! But then the transformed shape is an infinite extrusion!

We can't even just truncate the infinite extrusion in Union, because a Union of 2d shapes is a perfectly reasonable thing to do!

I guess sketches just show up as infinite extrusions? I have made the nodes able to report 2dness with is2d(), in future I guess we can make the nodes also say if they want 2d or 3d children? Forget it for now, infinite extrusions is OK.

Domain repetition

So the plan with this is to make every node be able to give a centre and radius for a bounding sphere. The default will be infinite. And then in linear pattern etc. we only need to do a union of as many copies as fit inside one bounding sphere, and use domain repetition for the rest.

Let's say the bounding sphere has radius 5, and the spacing is 8. Then we know that the bounding spheres overlap, because 2*radius < spacing.

For a first pass, we can do domain repetition if 2*radius <= spacing, and explicit union otherwise.

It works if I make it always space in the Z axis, but how do I make it step in other axes?

Oh, this is not working right because my coordinate system is somehow left-handed. That may be also why other coordinate stuff wasn't working very well.

I may have fixed it. Hmm, no, I think it is still left-handed.

Isoform todo

General-purpose SDF evaluation

• check out whether https://github.com/mkeeter/fidget/tree/wgpu-bytecode is worth using
  • decide whether I can get away with only having GLSL SDF implementations
  • if so: sketch out a GLSL sparse voxel octree generator & revert the commit that added them
  • if not: fix all the JavaScript SDF implementations (including make sure everything is a Vec3 where it needs to be)
• show the coordinates of the surface under the cursor
• marching cubes to make an STL file

Sketcher workflow

• fillet the top/bottom of the extrusion
• make SketchNode support arcs
• a way to view the SDF "rings" in the sketcher
• allow creating datum points/lines/planes
• allow "attaching" sketches to datum planes
• allow padding along a datum line
• allow filleting at top or bottom of Pad, and separate radii on each?
• allow draft angle on Pad
• constraint solver
• stop un-extruded sketches from looking like infinite extrusions

Domain repetition

• make it limit to the number of copies
• also use it for Mirror, PolarPattern
• also use it with an explicit union of a small number of copies, in cases where the bounding boxes do overlap

Performance

• only requestAnimationFrame() if the pan/zoom/document etc. has changed, no need to redraw the same frame over and over again
• show shader compile time, and frame render time instead of fps
• always consider bounding boxes in combinators and skip children that can't possibly affect the outcome (e.g. in union the box is further than current dist, or in smooth union the box is further than current dist plus blend radius, etc.)
• the rotateToAxis/transposeMatrix matrix calculations can be done in JavaScript instead of in the shader

UX

• draggable Transform node
• show local origin & axes when rendering secondary node
• some way to make the secondary node stick on even when clicked off
• some way to stop rendering the whole document and just act as if the root is some other node, probably grey out the rest of the tree when this is done, as if the rest were "Disabled"
• save/load your work
• expose shader compilation warnings to the user
• allow reduced opacity, start raymarching through the internal space by reversing the distances
• should smoothK be renamed to blendRadius? filletRadius? If it doesn't act like a radius, can we make it one? If not, what else should we call it?

Parametric design

• allow defining formulae for properties, separately from evaluating expressions
• formulae can reference properties of other objects (force displayName to be unique?)
• allow defining new parameters in a VarSet or something

New primitives

• involute gear
• bend
• Groove combinator? Can be additive or subtractive, https://forgedthoughts.com/modeling/booleans/index.html
• text

Research areas

• can we do targeted fillets/chamfers?
• can we do the thing I mentioned yesterday where we somehow use domain deforming functions to deform the locations of a Pattern (translation and rotation), but still use the un-deformed child tree but just place them at those locations?