Redrawing gl2 isigraphs using event handler - j

Question

I've been playing around with the table & gl2 demos, and have come across a "domain error: chkgl2" multiple times.
What I'm trying to do is to modify an isigraph after its initialized on program run, by selecting / un-selecting a checkbox.
I have the following code:
demo_run=: 3 : 0
require 'gl2'
coinsert 'jgl2'
wd 'pc test closeok escclose'
wd 'pn "Tester"'
wd 'cc gs isigraph'
wd 'cc cb checkbox; cn "Test GUI"'
wd 'set cb value 0'
wd 'pmove 400 10 400 200'
wd 'pshow'
)
demo_cb_button=: 3 : 0
demo_gs_paint''
)
demo_gs_paint=: 3 : 0
'w h'=: glqwh''
glfill 0 0 0 255
glrgb 255 223 0
glpen 2 1
if. cb do.
for_i. 250*i. >. h%250 do.
gllines 0,i,w,i
end.
end.
)
demo_run''
What I'm expecting to happen is the checkbox to update the isigraph. What I'm getting is a "domain error: chkgl2" on line "glfill 0 0 0 255".
Any help would be appreciated!

Answer 1

A couple of things that I spotted:
1) you are calling your parent 'test' but you are giving the verbs a 'demo' prefix. You can do this for the verb demo_run, but if you want the children of the form to react you will need to refer to them in the form of test_cb_button
2) cb in your test is actually the character '1' and not the integer 1, so in order for it to work as a conditional you need to change it to an integer type. I used Do (".) to make this change (". cb)
3) I am not sure that your code 250*i. >. h%250 is doing what you expect, so I replaced it with i. >.h%15 and then changed the gllines command to gllines 0,i,w,i*15 for a more interesting effect.
4) You are using isigraph which automatically triggers the painting of the screen and I wonder if the fact that you are clicking a button which triggers drawing of a screen to change the button image while also explicitly requiring the painting of the screen using the test_gs_paint verb is causing the glfill to be run twice. The second time it may be in a context that creates a domain error. To be honest, I don't know. What I do know is that when I use isidraw instead and trigger my own paint command using glpaint '' (which isidraw requires) that things seem to work.
5) I have added a second version that works with isigraph and it looks as if the issue is that by calling the paint verb directly with test_gs_paint that you were indeed calling it twice. By changing the action to glpaint '', the form does rerun the painting of the entire form once and this causes test_gs_paint to update as well. This time though it does it in a more coordinated fashion. My second version reflects the change. Other corrections I have left in place.
My isidraw version of the code follows:
demo_run=: 3 : 0
require 'gl2'
coinsert 'jgl2'
wd 'pc test closeok escclose'
wd 'pn "Tester"'
wd 'cc gs isidraw' NB. changed from isigraph
wd 'cc cb checkbox; cn "Test GUI"'
wd 'set cb value 0'
wd 'pmove 400 10 400 200'
wd 'pshow'
)
test_cb_button=: 3 : 0
test_gs_paint''
)
test_gs_paint=: 3 : 0
'w h'=: glqwh''
glfill 0 0 0 255
glrgb 255 223 0
glpen 2 1
if. (".cb) do. NB. needed to test on an integer and not a character value
for_i. i. >.h%15 do. NB. changed to give a more noticeable effect
gllines 0,i,w,i*15
end.
end.
glpaint'' NB. added to accommodate isidraw requirement of explicit painting
)
demo_run''
My isigraph version of the form:
demo_run=: 3 : 0
require 'gl2'
coinsert 'jgl2'
wd 'pc test closeok escclose'
wd 'pn "Tester"'
wd 'cc gs isigraph'
wd 'cc cb checkbox; cn "Test GUI"'
wd 'set cb value 0'
wd 'pmove 400 10 400 200'
wd 'pshow'
)
test_cb_button=: 3 : 0
glpaint '' NB. changed from test_gs_paint ''
)
test_gs_paint=: 3 : 0
'w h'=: glqwh''
glfill 0 0 0 255
glrgb 255 223 0
glpen 2 1
if. (".cb) do.
for_i. i. >.h%15 do.
gllines 0,i,w,i*15
end.
end.
)
demo_run''