$\mathrm{with}\left(\mathrm{DocumentTools}:-\mathrm{Canvas}\right)\:$

lines are always tied to groups; if a line is specified outside of a group, then a group is created

$\mathrm{cv}≔\mathrm{NewCanvas}\left(\left[''Line''\,x^2\,\mathrm{Line}\left(\left[\left[30\,40\right]\,\left[400\,40\right]\right]\right)\,y^2\right]\right)\:$

$\mathrm{ShareCanvas}\left(\mathrm{cv}\right)$

use the Group element to combine other elements together with the lines

$\mathrm{cv}≔\mathrm{NewCanvas}\left(\left[''Line''\,\mathrm{Group}\left(\left[x^2\,\mathrm{Line}\left(\left[\left[30\,40\right]\,\left[400\,40\right]\right]\right)\,y^2\right]\right)\right]\right)\:$

$\mathrm{ShareCanvas}\left(\mathrm{cv}\right)$

a matrix of (x,y) pairs can be used to draw shapes

$\mathrm{cv}≔\mathrm{NewCanvas}\left(\left[''Line''\,\mathrm{Group}\left(\left[x^2\,\mathrm{Line}\left(⟨⟨55|0⟩\,⟨55|40⟩\,⟨90|40⟩\,⟨90|0⟩\,⟨55|0⟩⟩\right)\,y^2\right]\right)\right]\right)\:$

$\mathrm{ShareCanvas}\left(\mathrm{cv}\right)$

$\mathrm{with}\left(\mathrm{DocumentTools}:-\mathrm{Canvas}\right)\:$

create or fetch a canvas with lines in it, then view them in Maple

$\mathrm{cv}≔\mathrm{NewCanvas}\left(\left[''Line''\,\mathrm{Group}\left(\left[x^2\,\mathrm{Line}\left(⟨⟨55|0⟩\,⟨55|40⟩\,⟨90|40⟩\,⟨90|0⟩\,⟨55|0⟩⟩\,\mathrm{color}=''\#FF0000''\right)\,\mathrm{Line}\left(⟨⟨55|10⟩\,⟨90|10⟩⟩\,\mathrm{thickness}=20\,\mathrm{\alpha }=255\,\mathrm{color}=''yellow''\right)\,y^2\right]\right)\right]\right)\:$

$M≔\mathrm{GetElements}\left(\mathrm{cv}\,''line''\right)\:$$\mathrm{numelems}\left(M\right)$

$\mathrm{plots}:-\mathrm{display}\left(\mathrm{seq}\left(\mathrm{elem}:-\mathrm{plot}\left(\mathrm{elem}\,\mathrm{view}=\left[-10..10\,-10..10\right]\right)\,\mathrm{elem}=M\right)\right)$

In this section we create an app that allows you to draw on a blank plot, then do a curve fit of the sketch Note: drawing is done using the Pen tool in Maple Learn.  The Pen tool had not been released in the Production version of Maple Learn at the time of writing this example (hopefully it will be there when you try this)

$\mathrm{with}\left(\mathrm{DocumentTools}:-\mathrm{Canvas}\right)\:$

Fit := proc( canvas )
   local M := GetElements(canvas,"line"):
   local sc := Script();
   SetActive(sc,"3:0");
   if numelems(M) =  0 then
       SetText(sc,"No lines were drawn");
   elif numelems(M) > 1 then
       SetText(sc,"Multiple lines were drawn, clear your drawing and try again with just one smooth curve");
   else
       local data := M[1]:-convertToPlotData( M[1], offset=0, view=[-10..10,-10..10] );
       local f, a1, b1, c1, d1;
       f := CurveFitting:-LeastSquares( data, x, 'curve' = a1+b1*x+c1*x^2+d1*x^3 );
       SetText(sc,"Your curve looks like: ");
       SetMath(sc,f,'where'="below");
       SetActive(sc,"1:0");
       SetPlot(sc,plot(f,view=[-10..10,-10..10]));
   end if;
   ToString(sc);
end proc:

$\mathrm{cv}≔\mathrm{NewCanvas}\left(\left[''Sketch:''\,\mathrm{StaticPlot}\left(\right)\,\mathrm{ScriptButton}\left(''Apply\; LeastSquares\; Fit''\,\mathrm{Fit}\,\mathrm{position}=\left[570\,92\right]\right)\,\mathrm{Group}\left(\left[\mathrm{Text}\left(''Draw\; a\; line\; on\; the\; plot\; area\; using\; the\; pen\; tool\; then\; click\; the\; button\; above''\right)\right]\,\mathrm{position}=\left[550\,132\right]\right)\right]\right)\:$

$\mathrm{ShareCanvas}\left(\mathrm{cv}\right)$