hello!

can you tell me please how to
1) make the disc in the attached file convex
2) afterwards convert the disc into a cross (that will retain the convex effect)

thanks!

Hi user,
Just to be clear, "convex" will make it sort of bubblish or balloony. So that you want a bubblish, or puffy looking cross, correct? (concave would make it sunken in the middle) Do you have an example of what you want it to look like when it's finished?

The reason I'm asking about that, is because I'm not sure what kind of effect you want, and there might be more than one way to do it. Also, I don't understand why you need to have this disc converted to a cross, rather than just draw a cross and apply the puffy effect to it. That would probably be much easier

Having said all that though, I'm not sure Inkscape would be the best program to do this. Blender might actually be better for this, since it sounds like you need some kind of 3D effect. You could look into Blender.

Sticking with Inkscape though, there probably is a filter that will make things look puffy. I think ivan louette maybe has one at Open Clipart Library (search "ivan_louette") but I can't remember for sure.....ok, let me have a look for myself..... Ok, there is one called "Bubble Your Pictures" but it's more like tiny bubbles or blisters, rather than make the object one big bubble. There might be some packed with Inkscape (in Filters menu) that might work. For example, there's one called Bubble Gum, that sounds like it might work....maybe with some tweaking.

To do it exactly like you said:
1 -- Find a filter that will create the convex effect, and apply it to the disc, or the ellipse on top of the disc.
2 -- Draw a cross to use as a clipping path, then Clip the disc with the cross path.

However, if you do it that way, you will lose the depth. You'll lose the parts of the disc that make appear 3D-ish, because they'll be clipped away. It will still be puffy, but not raised. I'm wondering if what you have in mind, is the disc kind of morphing into the cross, so that the cross still has the raised edge, like the disc does? If that's the case, you'd be better off drawing the cross first, and then applying the filter. The good news is that you would draw the cross just like you did the disc, except it would be a cross instead of an ellipse

You probably want to look up some basic instructions on perspective to understand how circles(discs) become ellipses in perspective and become flatter ellipses as they move toward a vanishing point. convex(spherical) objects are made of a half ellipse and a circular curve and therefore when small also require shading and other tricks to distinguish them from a disc in perspective. The substitution of another object (cross) with the same curvature requires much! more complicated procedure to draw accurately. I suggest you sketch it on paper and then just try to approximate it on screen. You could also use a raster program or a 3D progam and then trace the result in inkscape.
Later edit: Added a little section on how to flatten the curvature.

what I basically want is to replace this red disc with a red cross, retaining the convex-like effect, the thickness of the object, the diameter of the object, etc

is it better to cut the circle or to draw a cross from the begining? and how?

thanks!

as I said in my previous post it becomes quite difficult to do this accuretely, but it seems from the drawing you have that some inaccuracy in rendition is acceptable i.e., so why don't you just draw the cross on top of the disc, and then use the to bend the lines of the cross to approximate the curvature of the disc? All straight lines in the cross will be ellipses. The far side of the cross will also be much shorter, if at all visible.
You could also try using a GIMP filter and then tracing the result in Inkscape.This was a quick 'map object' filter application. It traced well in Inkscape... I edited it a bit, but basically this is what you would get.
Illustrator has some vector 3D mapping if you have access to a copy.

If you want a sort of rim on the cross, like there is on the disc... Ok, here, I've made a screenshot to illustrate. It's the blue object and the green object that I'm calling a rim. That's what gives the ellipse depth, and makes it look like a disc and not just a flat elllipse. It's what creates the illusion of 3D. If you want that kind of effect on the cross, you'd be better off drawing the cross from scratch.

That's because the disc can't be just morphed into a cross and keep the rim which gives the disc depth. Not with Inkscape anyway. With Inkscape, you could cut the cross out of the disc, but it would lose the rim. See how I've overlaid a cross shape on it? The cross could be drawn with the same perspective as the disc, but you'd still just be basically cutting it out of the disc.



The good news is that this disc gives you a clue how to draw the cross, right? With a cross like I drew, you could use the Perspective extension to make it look partially rotated around (like if you used a 3D modelling program like Blender). It wouldn't really be 3D, but it would look like 3D. Then you would just duplicate it twice. Move one duplicate (for the green object in my screenshot) below and slightly down and to the left. Then move the other duplicate to the bottom, and even further down and to the left, like for the blue object.

Then you also have clues from your 2nd SVG file, how to make it look convex. Just use that file and take it apart, to see how it was built. Use the status bar to identify which tool or feature was used. Darn, I've already closed that file, but I think the convex illusion was created with gradients. That file has everything you need, to make what you want. You just have to be a detective -- it's all there. You just need to draw the cross shape, do the duplicates like I said, to make it look 3D, and apply similar gradients.

You can do it! I have faith Just jump right in there with both feet. I actually used a grid to help me get the cross all straight and even. And the Perspective extension can work like magic. You don't have to be much of an artist to use Inksape. If you get stuck, just ask for help. We love to help

(Geez druban, you'd think we were psychically connected or something )

(Edit - Oops, I forgot to upload the screenshot)