# Please can I use sgl to draw to a bitmap
**URL:** https://racket.discourse.group/t/please-can-i-use-sgl-to-draw-to-a-bitmap/923
**Category:** General
**Created:** [April 25, 2022, 1:19pm UTC](https://racket.discourse.group/t/please-can-i-use-sgl-to-draw-to-a-bitmap/923 "2022-04-25T13:19:37Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@hendrikboom3](https://racket.discourse.group/u/hendrikboom3)
#### Post date: [April 25, 2022, 1:19pm UTC](https://racket.discourse.group/t/please-can-i-use-sgl-to-draw-to-a-bitmap/923/1 "2022-04-25T13:19:37Z")
I am currently using sgl to draw to a window, and using the screenshot progrm to convert the picture to a .png file.
Unfortunately, this seems to limut the png to screen size, and I need more pixels than that for my application.
So my guess is that I need to create an sgl-compatible opengl environment that draws to bitmap instead of a window, and then use the tools available to write that bitmap out as a .png file.
Trouble is, I don't know how to get a bitmap out of sgl.
Here's the function I use to create the window and call a function called drawer to draw into it.
```scheme
(define (environ drawer)
#;(printf "in environ\n")
(define my-canvas%
(class* canvas% ()
(inherit with-gl-context swap-gl-buffers)
(define/override (on-paint) ; When is on-paint caled?
(printf "on-paint ~s~n" (count))
(with-gl-context
(lambda ()
#;(printf "call drawer~n")
(drawer)
#;(printf "returned from drawer~n")
(swap-gl-buffers)
)
)
)
(define/override (on-size width height) ; Is this what is called when resizing the window with a mouse?
(with-gl-context
(lambda ()
(resize width height)
)
)
)
(super-instantiate () (style '(gl))) ; What is this?
)
)
#;(printf "before win~n")
(define win (new frame% (label "OpenGl Test")
(min-width 600)
(min-height 600)))
#;(printf "before my-canvas~n")
(define gl (new my-canvas% (parent win)))
#;(printf "before show~n")
(send win show #t) ; presumably this runs the on-paint method.
; But why does it get called three times?
#;(printf "out-environ~n")
)
```
Presumably I need to set up a canvas% or a drawing context differently.
And, of course make a bitmap of the right size. Documentation suggests there are different kinds of bitmaps, and I'm not sure either which to use.
-- hendrik
---
### Author:  [@ryanc](https://racket.discourse.group/u/ryanc)
#### Post date: [April 25, 2022, 3:44pm UTC](https://racket.discourse.group/t/please-can-i-use-sgl-to-draw-to-a-bitmap/923/2 "2022-04-25T15:44:12Z")
Based on the docs, I would expected something like the following to work:
```
(require racket/class racket/draw racket/gui)
(define b (make-gl-bitmap 400 400 (new gl-config%)))
(define dc (send b make-dc))
(define glc (send dc get-gl-context))
(send glc call-as-current drawer)
(send b save-file "out.png" 'png)
```
Does that work for you?
---
### Author:  [@hendrikboom3](https://racket.discourse.group/u/hendrikboom3)
#### Post date: [April 25, 2022, 4:35pm UTC](https://racket.discourse.group/t/please-can-i-use-sgl-to-draw-to-a-bitmap/923/3 "2022-04-25T16:35:08Z")
It works beautifully. Thank you.
And it's a lot simpler than I expected from my trail through the documentation.
I get the general drift; now it's time to look all this up in the documentation and understand exactly how these classes are related.
Thank you again.
-- hendrik