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Canvas & CGContext
https://www.purebasic.fr/english/viewtopic.php?f=19&t=47346
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Author:  wilbert [ Fri Aug 26, 2011 12:07 pm ]
Post subject:  Canvas & CGContext

Is it possible to get a CGContextRef for a PureBasic canvas inside StartDrawing(CanvasOutput( )).
It would be great if it were possible to use OS X drawing functions to draw curves etc.

Author:  freak [ Fri Aug 26, 2011 5:01 pm ]
Post subject:  Re: Canvas & CGContext

There is no CGContext. The drawing is done by direct pixel manipulation in memory.

Author:  wilbert [ Fri Aug 26, 2011 7:30 pm ]
Post subject:  Re: Canvas & CGContext

Thanks for the answer.
I hoped it would be possible. I guess the only workaround is to create a cgimage and draw that onto the canvas.

Author:  wilbert [ Sat Aug 27, 2011 8:22 am ]
Post subject:  Re: Canvas & CGContext

Is it allowed to create a context like this ?

Code:
Structure ColorComponents
  r.f
  g.f
  b.f
  a.f
EndStructure

ImportC ""
 
  ; colorspace functions
  CGColorSpaceCreateDeviceRGB()
  CGColorSpaceRelease(colorspace)
 
  ; bitmapcontext functions
  CGBitmapContextCreate(*bdata, width, height, bitsPerComponent, bytesPerRow, colorspace, bitmapInfo)
  CGContextRelease(context)
 
  ; cgcontext functions to init and restore / release some things
  CGContextSaveGState(context)
  CGContextRestoreGState(context)
  CGContextScaleCTM(context, sx.f, sy.f)
  CGContextTranslateCTM(context, tx.f, ty.f)
  CGContextSetStrokeColorSpace(context, colorspace)
  CGContextSetFillColorSpace(context, colorspace)
 
  ; cgcontext drawing related functions
 
  CGContextSetStrokeColor(context, color)
  CGContextSetFillColor(context, color)
 
  CGContextClearRect(context, x.f, y.f, w.f, h.f)
 
  CGContextBeginPath(context)
  CGContextMoveToPoint(context, x.f, y.f)
  CGContextAddLineToPoint(context, x.f, y.f)
  CGContextAddArc(context, x.f, y.f, radius.f, startAngle.f, endAngle.f, clockwise)
  CGContextClosePath(context)
  CGContextStrokePath(context)
  CGContextFillPath(context)
 
  CGContextSetShadow(context, x_offset.f, y_offset.f, blur.f)
 
  CGContextFillRect(context, x.f, y.f, w.f, h.f)
 
EndImport

Procedure RenderOnCanvas(canvas)
 
  Protected cv_w, cv_h, csRGB, ctx
  Protected color.ColorComponents
 
  If StartDrawing(CanvasOutput(canvas))
   
    ; init some things
    cv_w = OutputWidth()
    cv_h = OutputHeight()
    csRGB = CGColorSpaceCreateDeviceRGB()
    ctx = CGBitmapContextCreate(DrawingBuffer(), cv_w, cv_h, 8, cv_w << 2, csRGB, 1)
    CGContextScaleCTM(ctx, 1, -1)
    CGContextTranslateCTM(ctx, 0, -cv_h)
    CGContextSetStrokeColorSpace(ctx, csRGB)
    CGContextSetFillColorSpace(ctx, csRGB)
   
    ; actual drawing
    CGContextSetShadow(ctx, 2, -2, 2)
    color\r = 1
    color\g = 0.5
    color\b = 0
    color\a = 1
    CGContextSetFillColor(ctx, color)
    CGContextFillRect(ctx, 5, 5, 50, 50)
   
    color\r = 0.5
    color\g = 1
    color\b = 0
    color\a = 1
    CGContextSetFillColor(ctx, color)
    CGContextBeginPath(ctx)
    CGContextAddArc(ctx, 80, 80, 25, 0, #PI, #True)
    CGContextFillPath(ctx)
   
    ; release some things
    CGContextRelease(ctx)
    CGColorSpaceRelease(csRGB)
    StopDrawing()
   
  EndIf
 
EndProcedure

If OpenWindow(0, 0, 0, 320, 220, "CanvasGadget", #PB_Window_SystemMenu | #PB_Window_ScreenCentered)
 
  CanvasGadget(0, 10, 10, 300, 200)
  RenderOnCanvas(0)
 
  Repeat
    Event = WaitWindowEvent()
  Until Event = #PB_Event_CloseWindow
 
EndIf

Author:  J. Baker [ Sat Aug 27, 2011 8:59 am ]
Post subject:  Re: Canvas & CGContext

Awesome wilbert! I was just reading about this earlier. Thanks! ;)

Author:  freak [ Sat Aug 27, 2011 10:13 am ]
Post subject:  Re: Canvas & CGContext

wilbert wrote:
Is it allowed to create a context like this ?


The fact that StartDrawing() returns the pixel data pointer for the canvas on OSX is not documented. While i don't think this will really change, its not good to rely on it. If you use the DrawingBuffer() command, you will get the same pointer but it will be more future proof.

Nice work btw.

Author:  wilbert [ Sat Aug 27, 2011 5:34 pm ]
Post subject:  Re: Canvas & CGContext

Thanks Freak.
I changed it so it's compatible now :D
It also works on images if you use ImageOutput instead of CanvasOutput.

A little note ...
The coordinate space of a CGContext is vertically flipped comparing to that of PureBasic.
To make it in line with what PureBasic uses, I used CGContextScaleCTM and CGContextTranslateCTM.
This doesn't affect the shadow so the y_offset of the shadow is a bit illogical now.

Author:  wilbert [ Sun Aug 28, 2011 5:47 am ]
Post subject:  Re: Canvas & CGContext

I simplified some things and added some more imports

cgcontext.pbi
Code:
Enumeration
  #kCGLineJoinMiter
  #kCGLineJoinRound
  #kCGLineJoinBevel
EndEnumeration

Enumeration
  #kCGLineCapButt
  #kCGLineCapRound
  #kCGLineCapSquare
EndEnumeration

Enumeration
  #kCGPathFill
  #kCGPathEOFill
  #kCGPathStroke
  #kCGPathFillStroke
  #kCGPathEOFillStroke
EndEnumeration

Enumeration
  #kCGBlendModeNormal
  #kCGBlendModeMultiply
  #kCGBlendModeScreen
  #kCGBlendModeOverlay
  #kCGBlendModeDarken
  #kCGBlendModeLighten
  #kCGBlendModeColorDodge
  #kCGBlendModeColorBurn
  #kCGBlendModeSoftLight
  #kCGBlendModeHardLight
  #kCGBlendModeDifference
  #kCGBlendModeExclusion
  #kCGBlendModeHue
  #kCGBlendModeSaturation
  #kCGBlendModeColor
  #kCGBlendModeLuminosity
EndEnumeration

ImportC ""
 
  ; colorspace functions
  CGColorSpaceCreateDeviceRGB()
  CGColorSpaceRelease(colorspace)
 
  ; bitmapcontext functions
  CGBitmapContextCreate(*bdata, width, height, bitsPerComponent, bytesPerRow, colorspace, bitmapInfo)
  CGContextRelease(context)
 
  ; cgcontext functions to init and restore / release some things
  CGContextSaveGState(context)
  CGContextRestoreGState(context)
  CGContextScaleCTM(context, sx.f, sy.f)
  CGContextTranslateCTM(context, tx.f, ty.f)
  CGContextSetStrokeColorSpace(context, colorspace)
  CGContextSetFillColorSpace(context, colorspace)
  CGContextSetStrokeColor(context, color)
  CGContextSetFillColor(context, color)
 
  ; cgcontext drawing related functions
  CGContextAddArc(context, x.f, y.f, radius.f, startAngle.f, endAngle.f, clockwise)
  CGContextAddArcToPoint(context, x1.f, y1.f, x2.f, y2.f, radius.f)
  CGContextAddCurveToPoint(context, cp1x.f, cp1y.f, cp2x.f, cp2y.f, x.f, y.f)
  CGContextAddEllipseInRect(context, x.f, y.f, w.f, h.f)
  CGContextAddLineToPoint(context, x.f, y.f)
  CGContextAddQuadCurveToPoint(context, cpx.f, cpy.f, x.f, y.f)
  CGContextAddRect(context, x.f, y.f, w.f, h.f)
  CGContextBeginPath(context)
  CGContextClearRect(context, x.f, y.f, w.f, h.f)
  CGContextClosePath(context)
  CGContextDrawImage(context, x.f, y.f, w.f, h.f, image)
  CGContextDrawPath(context, mode)
  CGContextDrawTiledImage(context, x.f, y.f, w.f, h.f, image)
  CGContextFillEllipseInRect(context, x.f, y.f, w.f, h.f)
  CGContextFillPath(context)
  CGContextFillRect(context, x.f, y.f, w.f, h.f)
  CGContextMoveToPoint(context, x.f, y.f)
  CGContextSetAlpha(context, alpha.f)
  CGContextSetBlendMode(context, mode)
  CGContextSetLineCap(context, cap)
  CGContextSetLineJoin(context, join)
  CGContextSetLineWidth(context, width.f)
  CGContextSetMiterLimit(context, limit.f)
  CGContextSetShadow(context, x_offset.f, y_offset.f, blur.f)
  CGContextSetShadowWithColor(context, x_offset.f, y_offset.f, blur.f, cgcolor)
  CGContextStrokeEllipseInRect(context, x.f, y.f, w.f, h.f)
  CGContextStrokePath(context)
  CGContextStrokeRect(context, x.f, y.f, w.f, h.f)
  CGContextStrokeRectWithWidth(context, x.f, y.f, w.f, h.f, width.f)
 
EndImport

Procedure CGContextCreate(flipped = #True)
  Protected w, h, csRGB, ctx
  w = OutputWidth()
  h = OutputHeight()
  csRGB = CGColorSpaceCreateDeviceRGB()
  ctx = CGBitmapContextCreate(DrawingBuffer(), w, h, 8, w << 2, csRGB, 1)
  If flipped
    CGContextScaleCTM(ctx, 1, -1)
    CGContextTranslateCTM(ctx, 0, -h)
  EndIf
  CGContextSetStrokeColorSpace(ctx, csRGB)
  CGContextSetFillColorSpace(ctx, csRGB)
  CGColorSpaceRelease(csRGB)
  ProcedureReturn ctx
EndProcedure

Procedure CGContextSetStrokeColorRGB(ctx, r.f, g.f, b.f, a.f = 1.0)
  CGContextSetStrokeColor(ctx, @r)
EndProcedure

Procedure CGContextSetFillColorRGB(ctx, r.f, g.f, b.f, a.f = 1.0)
  CGContextSetFillColor(ctx, @r)
EndProcedure

Procedure CGContextClearShadow(ctx)
  CGContextSetShadowWithColor(ctx, 0, 0, 0, #Null)
EndProcedure


test code
Code:
IncludeFile "cgcontext.pbi"

Procedure RenderOnCanvas(canvas)
 
  Protected ctx
 
  If StartDrawing(CanvasOutput(canvas))
   
    ; create a context
    ctx = CGContextCreate()
   
    ; drawing
    CGContextSetShadow(ctx, 2, -2, 2)
    CGContextSetFillColorRGB(ctx, 1, 0.5, 0)
    CGContextFillRect(ctx, 5, 5, 50, 50)
    CGContextFillRect(ctx, 105, 105, 50, 50)
    CGContextSetStrokeColorRGB(ctx, 0.9, 0.9, 0)
    CGContextSetFillColorRGB(ctx, 0.5, 1, 0)
    CGContextSetLineWidth(ctx, 2)
    CGContextClearShadow(ctx)
    CGContextBeginPath(ctx)
    CGContextAddArc(ctx, 80, 80, 25, #PI, 0, #True)
    CGContextAddQuadCurveToPoint(ctx, 130, 120, 105, 140)
    CGContextAddQuadCurveToPoint(ctx, 80, 160, 40, 140)
    CGContextDrawPath(ctx, #kCGPathFillStroke)
   
    ; release context and stop drawing
    CGContextRelease(ctx)
    StopDrawing()
   
  EndIf
 
EndProcedure

If OpenWindow(0, 0, 0, 320, 220, "CanvasGadget", #PB_Window_SystemMenu | #PB_Window_ScreenCentered)
 
  CanvasGadget(0, 10, 10, 300, 200)
  RenderOnCanvas(0)
 
  Repeat
    Event = WaitWindowEvent()
  Until Event = #PB_Event_CloseWindow
 
EndIf

Author:  netmaestro [ Sun Aug 28, 2011 7:18 am ]
Post subject:  Re: Canvas & CGContext

I wish I had a mac so I could see how this looks. Any chance you could post a screenshot?

Author:  wilbert [ Sun Aug 28, 2011 7:58 am ]
Post subject:  Re: Canvas & CGContext

It doesn't show much Netmaestro. :oops:
I made it a little more complicated so it shows at least some curves. :)
Image
The advantage of CGContext functions is that you can draw arcs, curves, use blend modes, transparency and that everything is antialiased.
It should make it easier to create better looking canvas examples.

Author:  Christian [ Tue Feb 14, 2017 11:08 am ]
Post subject:  Re: Canvas & CGContext

Hi there,

I compiled this code (PB 5.51), but it only shows a blank canvas. Is it supposed to work still or do internal changes in PB made since 2011 make it impossible?

Author:  wilbert [ Tue Feb 14, 2017 11:17 am ]
Post subject:  Re: Canvas & CGContext

The drawing function imports in its current form are only working on the 32 bit version of PureBasic.
Making it work on x64 isn't straightforward and would require a lot of changes.

If it has enough functionality for you, I recommend using the PureBasic VectorDrawing library.
It wasn't available when the code was created but serves more or less the same purpose and has the advantage of being cross platform.

Author:  Christian [ Tue Feb 14, 2017 11:30 am ]
Post subject:  Re: Canvas & CGContext

Thanks Wilbert.

Actually I was not to much in the Path-Function. I was rather looking for a way to make the CanvasGadget display in Retina resolution. Thought that the CGContext* functions might be a possibility, when adjusting the NSSize of the image (as suggested in viewtopic.php?p=442611#p442611, which works perfectly for a ImageGadget) and drawing the image it directly on the canvas CGContextRef.

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