[cairo] Qahirah: A High-Level Cairo API Binding For Python 3

[Olaf Schmidt]

Am 10.03.2015 um 01:09 schrieb Lawrence D'Oliveiro:

> I have done enhancements to my alhambra_tiles script to
> demonstrate some of the range of family variation.
> Feel free to keep up.

Ok - let's see...

Your current routine for the ArrowWing-Pattern is about 55 lines.
The selfcontained-routine below (including also PngFile-Output) is:

- significantly less voluminous (only about 35 lines)
- in my opinion easier to understand (math- or construction-wise)
- much easier to port to the flat C-API (straight cairo-default-stuff)


Sub RenderArrowPattern(FileName$, Optional Zoom=1, Optional Tilt=0, _
                                   Optional AFac=1, Optional RFac=1)
Dim R As Double, A As Double, Pat As cCairoPattern

   With Cairo.CreateSurface(400, 400).CreateContext

     .PushGroup , 0, 0, 48 * Zoom, 48 * Zoom
     .ScaleDrawings Zoom, Zoom
     .TranslateDrawings 24, 24 'shift into the center of the PushGroup

     A = 0.5 * Atn(1) * AFac 'AFac influences the start-angle
     R = 12 * RFac 'RFac influences the Radius, RFac=4 equals TileSize

     .MoveTo -24, -24 'construct left-part from TopLeft
       A = A + 6 * Atn(1): .LineTo R * Cos(A), R * Sin(A)
       .LineTo 0, 0
       A = A + 6 * Atn(1): .LineTo R * Cos(A), R * Sin(A)
     .LineTo -24, 24

     .MoveTo 24, 24 'construct right-part from BottomRight
       A = A + 6 * Atn(1): .LineTo R * Cos(A), R * Sin(A)
       .LineTo 0, 0
       A = A + 6 * Atn(1): .LineTo R * Cos(A), R * Sin(A)
     .LineTo 24, -24

     .FillRule = CAIRO_FILL_RULE_EVEN_ODD
     .Fill , Cairo.CreateSolidPatternLng(vbBlack)

     Set Pat = .PopGroup(True, CAIRO_EXTEND_REFLECT)
     Set Pat.Matrix = Pat.Matrix.RotateCoordsDeg(Tilt)

     .Paint , Cairo.CreateSolidPatternLng(vbWhite)
     .Paint , Pat
     .Surface.WriteContentToPngFile FileName
   End With
End Sub


It produces fully "symmetrically reflected" Tile-Parts- and offers
influence over 4 optional Params (Zoom, Tilt, AngleFac, RadiusFac)

Here's some Demo-Output:

'defaults (no Tilt, all Factors as Zoom etc. at 1)
RenderArrowPattern "c:\temp\Arrow1.png"
http://vbRichClient.com/Downloads/Arrow1.png

'Zoom 0.25, Tilt 45°, AngleFactor = 0.6, RadiusFactor = 2.2
RenderArrowPattern "c:\temp\Arrow2.png", 0.25, 45, 0.6, 2.2
http://vbRichClient.com/Downloads/Arrow2.png

'Zoom 1.5, Tilt 45°, AngleFactor = 2, RadiusFactor = 2.5
RenderArrowPattern "c:\temp\Arrow3.png", 1.5, 45, 2, 2.5
http://vbRichClient.com/Downloads/Arrow3.png

'Zoom 2.5, no Tilt, AngleFactor = 4.5, RadiusFactor = 4.5
RenderArrowPattern "c:\temp\Arrow4.png", 2.5, 0, 4.5, 4.5
http://vbRichClient.com/Downloads/Arrow4.png

So, as far as your "keeping up" goes - I'm not really sure
how often we want to repeat the same exercise.

I mean, the extended vector- and matrix-support in your Python-
Wrapper is "nice to have" - but apparently when used for the
"problem at hand", it's (as demonstrated) less efficient code-wise,
compared to "working more near to the original cairo-API with
simple trigonometric math".


Olaf