Hi,
Guest
is render() a function or a module or an operator please
V
vulcan_@mac.com
Mon, Jul 28, 2025 11:15 PM
hi .. i reported a bug on the operation of what i thought was the render() module
and the feedback was that it was operating correctly .. but i still do not know what it does exactly, nor why it would be used. Why was the
I thought it a module because it returns no value (not a function !) and does accept braces “{}“ to expand its operation to a group of primatives
It does not create objects but it can add geometry in the form of additional triangles on an existing mesh witness the primitive spheres in the bug report.
But it does this selectively.
render() is called to solve visualization issues to do with unions/ intersections/ differences yes?
but why does it NOT do anything in some cases?
hi .. i reported a bug on the [operation of what i thought was the render() module](https://github.com/openscad/openscad/issues/6046 "operation of what i thought was the render() module")
and the feedback was that it was operating correctly .. but i still do not know what it does exactly, nor why it would be used. Why was the
I thought it a module because it returns no value (not a function !) and does accept braces “{}“ to expand its operation to a group of primatives
It does not create objects but it can add geometry in the form of additional triangles on an existing mesh witness the primitive spheres in the bug report.
But it does this selectively.
render() is called to solve visualization issues to do with unions/ intersections/ differences yes?
but why does it NOT do anything in some cases?
JB
Jordan Brown
Tue, Jul 29, 2025 5:13 AM
On 7/28/2025 4:15 PM, vulcan_--- via Discuss wrote:
and the feedback was that it was operating correctly .. but i still do
not know what it does exactly, nor why it would be used.
It processes its children and returns something basically equivalent to
a polyhedron().
I'm aware of two basic reasons for using it:
- It can "fix" some preview artifacts. It will usually fix
Z-fighting. (But I think it can also introduce convexity artifacts.) - It can improve preview zoom/pan/rotate performance. Preview
normally has to do its black magic on all of the operations in the
model, every time the camera moves. render() does the processing
and caches the result so, although it can take longer to be ready,
zoom/pan/rotate can be faster.
I thought it a module because it returns no value (not a function !)
and does accept braces “{}“ to expand its operation to a group of
primatives
It is unquestionably a module. It only exists in statement context, not
in expression context.
It does not create objects but it can add geometry in the form of
additional triangles on an existing mesh witness the primitive spheres
in the bug report.
Triangles of this sort are not geometry, except in the sense that the
sides of a polygon or the faces of a polyhedron are "geometry".
It never adds or removes volume from the model.
But it does this selectively.
It is an implementation detail exactly what polyhedron it generates, as
long as it's equivalent to the child operations. As a trivial example,
if presented with a cube it is an implementation detail whether it
leaves the faces as squares or splits them into triangles, and if it
splits them into triangles it is an implementation detail which diagonal
it will split on. (And as an implementation detail the program is free
to do something different tomorrow than it does today, or to do
different things in different situations.)
We do try to keep it doing the same thing in the same situation, mostly
for testability reasons.
render() is called to solve visualization issues to do with unions/
intersections/ differences yes?
Z-fighting, mostly, I think.
but why does it NOT do anything in some cases?
Because it doesn't need to, because the child is already equivalent to a
polyhedron().
On 7/28/2025 4:15 PM, vulcan_--- via Discuss wrote:
>
> and the feedback was that it was operating correctly .. but i still do
> not know what it does exactly, nor why it would be used.
>
It processes its children and returns something basically equivalent to
a polyhedron().
I'm aware of two basic reasons for using it:
* It can "fix" some preview artifacts. It will usually fix
Z-fighting. (But I think it can also introduce convexity artifacts.)
* It can improve preview zoom/pan/rotate performance. Preview
normally has to do its black magic on all of the operations in the
model, every time the camera moves. render() does the processing
and caches the result so, although it can take longer to be ready,
zoom/pan/rotate can be faster.
> I thought it a module because it returns no value (not a function !)
> and does accept braces “{}“ to expand its operation to a group of
> primatives
>
It is unquestionably a module. It only exists in statement context, not
in expression context.
> It does not create objects but it can add geometry in the form of
> additional triangles on an existing mesh witness the primitive spheres
> in the bug report.
>
Triangles of this sort are not geometry, except in the sense that the
sides of a polygon or the faces of a polyhedron are "geometry".
It never adds or removes volume from the model.
> But it does this selectively.
>
It is an implementation detail exactly what polyhedron it generates, as
long as it's equivalent to the child operations. As a trivial example,
if presented with a cube it is an implementation detail whether it
leaves the faces as squares or splits them into triangles, and if it
splits them into triangles it is an implementation detail which diagonal
it will split on. (And as an implementation detail the program is free
to do something different tomorrow than it does today, or to do
different things in different situations.)
We do try to keep it doing the same thing in the same situation, mostly
for testability reasons.
> render() is called to solve visualization issues to do with unions/
> intersections/ differences yes?
>
Z-fighting, mostly, I think.
> but why does it NOT do anything in some cases?
>
Because it doesn't need to, because the child is already equivalent to a
polyhedron().
JB
Jordan Brown
Tue, Jul 29, 2025 5:20 AM
And answering question from the bug report...
My question then become, why bother having render() ? why not build
whatever it does into the rendering code so there is no mystery
visible to the user .. but that should be answered in a different forum
Ideally, it wouldn't be necessary.
Ideally, we'd always run the model through the full rendering engine,
and always produce a mesh.
But we do not live in an ideal world. Historically, the rendering
engine (CGAL) was enormously slower than the preview engine, and for
most models a pure preview is a better tradeoff. Also, historically the
rendering engine did not preserve color, and so if you wanted color in
the display of your model you needed to avoid it. Manifold has largely
addressed both of these, and so has become more practical as an "always"
option. (But: does Clipper preserve color in 2D operations?)
And answering question from the bug report...
> My question then become, why bother having render() ? why not build
> whatever it does into the rendering code so there is no mystery
> visible to the user .. but that should be answered in a different forum
>
Ideally, it wouldn't be necessary.
Ideally, we'd always run the model through the full rendering engine,
and always produce a mesh.
But we do not live in an ideal world. Historically, the rendering
engine (CGAL) was enormously slower than the preview engine, and for
most models a pure preview is a better tradeoff. Also, historically the
rendering engine did not preserve color, and so if you wanted color in
the display of your model you needed to avoid it. Manifold has largely
addressed both of these, and so has become more practical as an "always"
option. (But: does Clipper preserve color in 2D operations?)
V
vulcan_@mac.com
Wed, Jul 30, 2025 9:15 PM
ok .. how about this question:
what is the difference between
render() sphere();
there is no change to the sphere’s mesh
and
render() { t() sphere(); sphere(); t() sphere() }
where t() is translate to move the spheres out of the way of each other
but all three of the spheres are completely converted from quads to triangles
folks have said that there is a sort of implicit union done between all the shapes included in the scope of the render render() and that a single (?) mesh is made of all of them
is there a threshold .. how many quads does have the union have to have before they have to be split?
i have been playing with this script ..
applying render to one object does not change it,
but for two or more, whether they are intersecting or not .. then they get converted to triangles
i changed the shapes to cubes .. if just one follows the render it is not divided, but two or more, even when not intersecting (i removed the yellow stretched out cube so only the 3 colored ones were left) their sides don’t get turned into triangles
so is it just the number of shapes in the “union” ? is the rule - only one shape in the “union” do nothing ? two or more start making triangles?
ok .. how about this question:
what is the difference between
`render() sphere();`
there is no change to the sphere’s mesh
and
`render() { t() sphere(); sphere(); t() sphere() }`
where t() is translate to move the spheres out of the way of each other
but all three of the spheres are completely converted from quads to triangles
folks have said that there is a sort of implicit union done between all the shapes included in the scope of the render render() and that a single (?) mesh is made of all of them
is there a threshold .. how many quads does have the union have to have before they have to be split?
i have been playing with this script ..
applying render to one object does not change it,
but for two or more, whether they are intersecting or not .. then they get converted to triangles
i changed the shapes to cubes .. if just one follows the render it is not divided, but two or more, even when not intersecting (i removed the yellow stretched out cube so only the 3 colored ones were left) their sides don’t get turned into triangles
so is it just the number of shapes in the “union” ? is the rule - only one shape in the “union” do nothing ? two or more start making triangles?
NH
nop head
Wed, Jul 30, 2025 9:32 PM
render() is a module to make single mesh out of CSG. . If it is already a
single mesh render() does nothing because it is already a mesh. All
primitive solids are single meshes.
If there is CGS operations, such as implicit union, which you have there
then it uses CGAL or Manifold to do the CSG operation and those libraries
might change the triangulation. I think CGAL is happy with quads but
manifold uses triangles but I might be wrong about the latter.
On Wed, 30 Jul 2025 at 22:15, vulcan_--- via Discuss <
discuss@lists.openscad.org> wrote:
ok .. how about this question:
what is the difference between
render() sphere();
there is no change to the sphere’s mesh
and
render() { t() sphere(); sphere(); t() sphere() }
where t() is translate to move the spheres out of the way of each other
but all three of the spheres are completely converted from quads to
triangles
folks have said that there is a sort of implicit union done between all
the shapes included in the scope of the render render() and that a single
(?) mesh is made of all of them
is there a threshold .. how many quads does have the union have to have
before they have to be split?
i have been playing with this script ..
applying render to one object does not change it,
but for two or more, whether they are intersecting or not .. then they get
converted to triangles
i changed the shapes to cubes .. if just one follows the render it is not
divided, but two or more, even when not intersecting (i removed the yellow
stretched out cube so only the 3 colored ones were left) their sides don’t
get turned into triangles
so is it just the number of shapes in the “union” ? is the rule - only one
shape in the “union” do nothing ? two or more start making triangles?
OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org
render() is a module to make single mesh out of CSG. . If it is already a
single mesh render() does nothing because it is already a mesh. All
primitive solids are single meshes.
If there is CGS operations, such as implicit union, which you have there
then it uses CGAL or Manifold to do the CSG operation and those libraries
might change the triangulation. I think CGAL is happy with quads but
manifold uses triangles but I might be wrong about the latter.
On Wed, 30 Jul 2025 at 22:15, vulcan_--- via Discuss <
discuss@lists.openscad.org> wrote:
> ok .. how about this question:
>
> what is the difference between
>
> render() sphere();
>
> there is no change to the sphere’s mesh
>
> and
>
> render() { t() sphere(); sphere(); t() sphere() }
>
> where t() is translate to move the spheres out of the way of each other
>
> but all three of the spheres are completely converted from quads to
> triangles
>
> folks have said that there is a sort of implicit union done between all
> the shapes included in the scope of the render render() and that a single
> (?) mesh is made of all of them
>
> is there a threshold .. how many quads does have the union have to have
> before they have to be split?
>
>
> i have been playing with this script ..
>
> applying render to one object does not change it,
>
> but for two or more, whether they are intersecting or not .. then they get
> converted to triangles
>
> i changed the shapes to cubes .. if just one follows the render it is not
> divided, but two or more, even when not intersecting (i removed the yellow
> stretched out cube so only the 3 colored ones were left) their sides don’t
> get turned into triangles
>
> so is it just the number of shapes in the “union” ? is the rule - only one
> shape in the “union” do nothing ? two or more start making triangles?
> _______________________________________________
> OpenSCAD mailing list
> To unsubscribe send an email to discuss-leave@lists.openscad.org
>
V
vulcan_@mac.com
Thu, Jul 31, 2025 3:27 PM
the operation of render() is coming clear .. it is syntactically an operator module
it can appear last in a statement but then it does nothing, and if it is the only module in a statement it does nothing
i have not been able to find a way that it can be used in an expression
And i still feel that there is a conceptual bug here:
render() sphere();
leaves the sphere as quads with n-sided polygons at north and south ends
okay, i get that the sphere is a mesh and all the cool apps can handle quads so it is okay that render() does nothing.
So .. it should also do nothing for:
render() { sphere(); sphere(); sphere(); }
because if quads are good on the solo sphere why are quads no longer acceptable when i try to draw 3 spheres ? and please rem from my images that i was using translate to keep them from intersecting so there are no intersections nor joints to fix up
Why are quads converted to triangles at all?
the operation of render() is coming clear .. it is syntactically an operator module
it can appear last in a statement but then it does nothing, and if it is the only module in a statement it does nothing
i have not been able to find a way that it can be used in an expression
And i still feel that there is a conceptual bug here:
render() sphere();
leaves the sphere as quads with n-sided polygons at north and south ends
okay, i get that the sphere is a mesh and all the cool apps can handle quads so it is okay that render() does nothing.
So .. it should also do nothing for:
render() { sphere(); sphere(); sphere(); }
because if quads are good on the solo sphere why are quads no longer acceptable when i try to draw 3 spheres ? and please rem from my images that i was using translate to keep them from intersecting so there are no intersections nor joints to fix up
Why are quads converted to triangles at all?
NH
nop head
Thu, Jul 31, 2025 3:31 PM
When there are several children render doesn't know if they overlap or not
so it will always call the graphics library to do a union.
On Thu, 31 Jul 2025, 16:27 vulcan_--- via Discuss, <
discuss@lists.openscad.org> wrote:
the operation of render() is coming clear .. it is syntactically an
operator module
it can appear last in a statement but then it does nothing, and if it is
the only module in a statement it does nothing
i have not been able to find a way that it can be used in an expression
And i still feel that there is a conceptual bug here:
render() sphere();
leaves the sphere as quads with n-sided polygons at north and south ends
okay, i get that the sphere is a mesh and all the cool apps can handle
quads so it is okay that render() does nothing.
So .. it should also do nothing for:
render() { sphere(); sphere(); sphere(); }
because if quads are good on the solo sphere why are quads no longer
acceptable when i try to draw 3 spheres ? and please rem from my images
that i was using translate to keep them from intersecting so there are no
intersections nor joints to fix up
Why are quads converted to triangles at all?
OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org
When there are several children render doesn't know if they overlap or not
so it will always call the graphics library to do a union.
On Thu, 31 Jul 2025, 16:27 vulcan_--- via Discuss, <
discuss@lists.openscad.org> wrote:
> the operation of render() is coming clear .. it is syntactically an
> operator module
>
> it can appear last in a statement but then it does nothing, and if it is
> the only module in a statement it does nothing
>
> i have not been able to find a way that it can be used in an expression
>
> And i still feel that there is a conceptual bug here:
>
> render() sphere();
>
> leaves the sphere as quads with n-sided polygons at north and south ends
>
> okay, i get that the sphere is a mesh and all the cool apps can handle
> quads so it is okay that render() does nothing.
>
> So .. it should also do nothing for:
>
> render() { sphere(); sphere(); sphere(); }
>
> because if quads are good on the solo sphere why are quads no longer
> acceptable when i try to draw 3 spheres ? and please rem from my images
> that i was using translate to keep them from intersecting so there are no
> intersections nor joints to fix up
>
> Why are quads converted to triangles at all?
> _______________________________________________
> OpenSCAD mailing list
> To unsubscribe send an email to discuss-leave@lists.openscad.org
>
P
pca006132
Thu, Jul 31, 2025 5:26 PM
The API never said render will do nothing if the input is already a valid
mesh. We just say that the output is a valid mesh (that corresponds to the
input). There are many valid outputs.
On Thu, Jul 31, 2025, 23:32 nop head via Discuss discuss@lists.openscad.org
wrote:
When there are several children render doesn't know if they overlap or not
so it will always call the graphics library to do a union.
On Thu, 31 Jul 2025, 16:27 vulcan_--- via Discuss, <
discuss@lists.openscad.org> wrote:
the operation of render() is coming clear .. it is syntactically an
operator module
it can appear last in a statement but then it does nothing, and if it is
the only module in a statement it does nothing
i have not been able to find a way that it can be used in an expression
And i still feel that there is a conceptual bug here:
render() sphere();
leaves the sphere as quads with n-sided polygons at north and south ends
okay, i get that the sphere is a mesh and all the cool apps can handle
quads so it is okay that render() does nothing.
So .. it should also do nothing for:
render() { sphere(); sphere(); sphere(); }
because if quads are good on the solo sphere why are quads no longer
acceptable when i try to draw 3 spheres ? and please rem from my images
that i was using translate to keep them from intersecting so there are no
intersections nor joints to fix up
Why are quads converted to triangles at all?
OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org
OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org
The API never said render will do nothing if the input is already a valid
mesh. We just say that the output is a valid mesh (that corresponds to the
input). There are many valid outputs.
On Thu, Jul 31, 2025, 23:32 nop head via Discuss <discuss@lists.openscad.org>
wrote:
> When there are several children render doesn't know if they overlap or not
> so it will always call the graphics library to do a union.
>
> On Thu, 31 Jul 2025, 16:27 vulcan_--- via Discuss, <
> discuss@lists.openscad.org> wrote:
>
>> the operation of render() is coming clear .. it is syntactically an
>> operator module
>>
>> it can appear last in a statement but then it does nothing, and if it is
>> the only module in a statement it does nothing
>>
>> i have not been able to find a way that it can be used in an expression
>>
>> And i still feel that there is a conceptual bug here:
>>
>> render() sphere();
>>
>> leaves the sphere as quads with n-sided polygons at north and south ends
>>
>> okay, i get that the sphere is a mesh and all the cool apps can handle
>> quads so it is okay that render() does nothing.
>>
>> So .. it should also do nothing for:
>>
>> render() { sphere(); sphere(); sphere(); }
>>
>> because if quads are good on the solo sphere why are quads no longer
>> acceptable when i try to draw 3 spheres ? and please rem from my images
>> that i was using translate to keep them from intersecting so there are no
>> intersections nor joints to fix up
>>
>> Why are quads converted to triangles at all?
>> _______________________________________________
>> OpenSCAD mailing list
>> To unsubscribe send an email to discuss-leave@lists.openscad.org
>>
> _______________________________________________
> OpenSCAD mailing list
> To unsubscribe send an email to discuss-leave@lists.openscad.org
>
V
vulcan_@mac.com
Thu, Jul 31, 2025 10:39 PM
what does it matter that they overlap? or that a union is implicitly made when render() is applied to more than one shape?
your answer implies that a union being formed requires that all included shapes be converted to triangles .. why? what is wrong with the quads that the primitives are drawn in?
render() one shape .. no triangles. why not leave the quads on all of the shapes that don’t intersect anything ?
it probably seems that i am beating a dead horse here .. sorry for that. You folks seem to understand something about rendering in general that does not match what i know about it .. and know something about the inner workings of render() operator that is not at all obvious to someone outside the dev team
what does it matter that they overlap? or that a union is implicitly made when render() is applied to more than one shape?
your answer implies that a union being formed *requires* that all included shapes be converted to triangles .. why? what is wrong with the quads that the primitives are drawn in?
render() one shape .. no triangles. why not leave the quads on all of the shapes that don’t intersect anything ?
it probably seems that i am beating a dead horse here .. sorry for that. You folks seem to understand something about rendering in general that does not match what i know about it .. and know something about the inner workings of render() operator that is not at all obvious to someone outside the dev team
NH
nop head
Thu, Jul 31, 2025 10:47 PM
The quads to triangles are done by the geometry library that does the
union. I suspect you are using Manifold. I think if you select CGAl they
might remain as quads. Why you you care what they are? I don't often enable
show edges so I wouldn't notice.
On Thu, 31 Jul 2025, 23:42 vulcan_--- via Discuss, <
discuss@lists.openscad.org> wrote:
what does it matter that they overlap? or that a union is implicitly made
when render() is applied to more than one shape?
your answer implies that a union being formed requires that all
included shapes be converted to triangles .. why? what is wrong with the
quads that the primitives are drawn in?
render() one shape .. no triangles. why not leave the quads on all of the
shapes that don’t intersect anything ?
it probably seems that i am beating a dead horse here .. sorry for that.
You folks seem to understand something about rendering in general that does
not match what i know about it .. and know something about the inner
workings of render() operator that is not at all obvious to someone outside
the dev team
OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org
The quads to triangles are done by the geometry library that does the
union. I suspect you are using Manifold. I think if you select CGAl they
might remain as quads. Why you you care what they are? I don't often enable
show edges so I wouldn't notice.
On Thu, 31 Jul 2025, 23:42 vulcan_--- via Discuss, <
discuss@lists.openscad.org> wrote:
> what does it matter that they overlap? or that a union is implicitly made
> when render() is applied to more than one shape?
>
> your answer implies that a union being formed *requires* that all
> included shapes be converted to triangles .. why? what is wrong with the
> quads that the primitives are drawn in?
>
> render() one shape .. no triangles. why not leave the quads on all of the
> shapes that don’t intersect anything ?
>
> it probably seems that i am beating a dead horse here .. sorry for that.
> You folks seem to understand something about rendering in general that does
> not match what i know about it .. and know something about the inner
> workings of render() operator that is not at all obvious to someone outside
> the dev team
>
>
> _______________________________________________
> OpenSCAD mailing list
> To unsubscribe send an email to discuss-leave@lists.openscad.org
>
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