Eg put text on the cylinder surface, how can i call it, projection? shadow?
Of course we need transform the flat sharp into a curved one. I want put
many characters on the cylinder.

http://forum.openscad.org/file/n20182/test.png

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There's this quite old thingiverse thing, Write.scad:
https://www.thingiverse.com/thing:16193
But it's limited to using text supplied in a dxf file, rather than using
built in fonts.

I also found this update: https://github.com/brodykenrick/text_on_OpenSCAD
Which is  based on Write.scad but uses 'text ()'. Seems a bit complicated,
though!

I had a quick go at this, by slicing the text, then rotating the slices:

======

radius = 15;
height = 30;
slices = 20;

txt = "OpenSCAD";
text_depth = 2;

circumference = 2 * 3.14159 * radius;
slice_width = circumference / slices;

circular_text ();

module circular_text () {

union () {

    for (i = [0:1:slices]) {
        
        rotate ([0,0,i*(360/slices)]) translate ([0,-radius,0])

intersection () {

            translate ([-slice_width/2 - (i*slice_width) ,0 ,0]) rotate

([90,0,0])
linear_extrude(text_depth, center = true, convexity = 10)
text(txt);

            cube ([slice_width+0.1, text_depth+0.1, height], true);
        }
    }
}

}

======

This works pretty well, though if you increase the number of 'slices' to
improve the steps in the text, it takes a long time to draw/render! See the
OpenSCAD user manual for using 'text', to change size/font etc:
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Text

http://forum.openscad.org/file/n20185/text_on_cylinder.png

However, if I try to difference this from the cylinder, I get 'WARNING:
Normalized tree is growing past 10000 elements. Aborting normalization."

To get around this, I export the text as an stl, then reimport and
difference that from the cylinder:

======

difference () {
cylinder (r=radius, h=height, center=true);
import("text.stl", convexity=10);
}

======

http://forum.openscad.org/file/n20185/text_on_cylinder_2.png

I'm sure there are other ways of doing this, and it's probably been gone
over loads of times in the forum, but this seems a pretty straightforward to
me. You could even slice the words horizontally as well as vertically, and
map it onto a sphere.

Ian S.

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slicing the text using intersection() may be better. It seems more general
purpose and flexible. Sometimes maybe I need deal with a vertical text.

thanks all.

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See:
http://forum.openscad.org/textCylinder-dodgy-version-for-text-around-a-cylinder-td9262.html#a9265

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---======
include <size.def>;

font="经典繁毛楷,fan-maokai:style=Regular,maokai";
fsize=4;
text_depth = 2;

vspace=fsize*1.4;//不精确的数据, 手动调整测量
text_height=3;//不精确的数据, 手动调整测量

module char(unichar){
rotate([90,0,0])linear_extrude(text_depth)text(text=unichar,font=font,size=fsize);
}

module vtext(){
union(){
translate([0,0,vspace/23-text_height/2])char("御风而行");
translate([0,0,vspace/2-text_height/2])char("风");
translate([0,0,-vspace/2-text_height/2])char("而");
translate([0,0,-vspace/23-text_height/2])char("行");
}
//echo(len("御"));//1
}

radius = OR-text_depth/4;
height = h;
slices = 30;

//vtext();cube([22,1,8]);
string_width=22;//不精确的数据, 手动调整测量
actual_angle=360string_width/(23.14159*radius);
slice_width=string_width/slices;

module circular_text(){
union(){
for(i=[0:1:slices]){
rotate ([0,0,i*(actual_angle/slices)]) translate ([0,-radius,0])
intersection(){
translate([-slice_width/2-(i*slice_width),0,0])children();

cube([slice_width+0.1,text_depth+0.1,height],true);
        }
    }
}

}

//difference(){
#cylinder(height,r=OR,center=true);
circular_text()vtext();
//}

---=========

http://forum.openscad.org/file/n20189/2017-01-22_13-12-01%E5%B1%8F%E5%B9%95%E6%88%AA%E5%9B%BE.png

looks better. I found few problem:

1. Can not get accurate height or width of an string. I can only measure
   manually.
2. Can not do difference() if slices = 30. I got those message. Reduce
   slices make the output more ugly.

WARNING: Normalized tree is growing past 200000 elements. Aborting
normalization.
WARNING: Normalized tree is growing past 200000 elements. Aborting
normalization.
Compiling highlights (1 CSG Trees)...
WARNING: Normalized tree is growing past 200000 elements. Aborting
normalization.
WARNING: Normalized tree is growing past 200000 elements. Aborting
normalization.
Normalized CSG tree has 151 elements
Compile and preview finished.

3. Input unicode character in editor would mess up my code frequently. Maybe
   this is the IM's problem.

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My script DOES use intersection. Also, I had the same warnings. To get around
those, I rendered the text on it's own, exported it as stl, then reimported
it to difference from the cylinder. That works will.

Ian

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