Hi, Exploring the agg.py module of the matplotlib library, I
> have encauntered that I cannot represent smooth arcs. For
> example, circle appears as octagon. Could you give me an
> idea how to manage this and what is the reason for such
> behaviour? Here is the code of the agg_test.py changed to
> draw arc, but not giving the desired result:
Hi Zori,
I updated the agg_test.py example to show how to do a few more things
-- drawing curves, filling and stroking, and making affine
transformations of paths and curves. Down the road I would like to
replace refactor backend_agg.py and _backend_agg.cpp to use this swig
wrapper of agg, so that agg users would have access to the low level
agg library for customized drawing over a mpl figure.
# this example uses the agg python module directly there is no
# documentation -- you have to know how to use the agg c++ API to use
# it
import matplotlib.agg as agg
from math import pi
## Define some colors
red = agg.rgba8(255,0,0,255)
blue = agg.rgba8(0,0,255,255)
green = agg.rgba8(0,255,0,255)
black = agg.rgba8(0,0,0,255)
white = agg.rgba8(255,255,255,255)
yellow = agg.rgba8(192,192,255,255)
## Create the rendering buffer, rasterizer, etc
width, height = 600,400
stride = width*4
buffer = agg.buffer(width, height, stride)
rbuf = agg.rendering_buffer()
rbuf.attachb(buffer)
pf = agg.pixel_format_rgba(rbuf)
rbase = agg.renderer_base_rgba(pf)
rbase.clear_rgba8(blue)
renderer = agg.renderer_scanline_aa_solid_rgba(rbase);
renderer.color_rgba8( red )
rasterizer = agg.rasterizer_scanline_aa()
scanline = agg.scanline_p8()
## A polygon path
path = agg.path_storage()
path.move_to(10,10)
path.line_to(100,100)
path.line_to(200,200)
path.line_to(100,200)
path.close_polygon()
# stroke it
stroke = agg.conv_stroke_path(path)
stroke.width(3.0)
rasterizer.add_path(stroke)
agg.render_scanlines_rgba(rasterizer, scanline, renderer);
## A curved path
path = agg.path_storage()
path.move_to(200,10)
path.line_to(350,50)
path.curve3(150,200)
path.curve3(100,70)
path.close_polygon()
curve = agg.conv_curve_path(path)
# fill it
rasterizer.add_path(curve)
renderer.color_rgba8( green )
agg.render_scanlines_rgba(rasterizer, scanline, renderer);
# and stroke it
stroke = agg.conv_stroke_curve(curve)
stroke.width(5.0)
rasterizer.add_path(stroke)
renderer.color_rgba8( yellow )
agg.render_scanlines_rgba(rasterizer, scanline, renderer);
## Transforming a path
path = agg.path_storage()
path.move_to(0,0)
path.line_to(1,0)
path.line_to(1,1)
path.line_to(0,1)
path.close_polygon()
rotation = agg.trans_affine_rotation(pi/4)
scaling = agg.trans_affine_scaling(30,30)
translation = agg.trans_affine_translation(300,300)
trans = rotation*scaling*translation
transpath = agg.conv_transform_path(path, trans)
stroke = agg.conv_stroke_transpath(transpath)
stroke.width(2.0)
rasterizer.add_path(stroke)
renderer.color_rgba8( black )
agg.render_scanlines_rgba(rasterizer, scanline, renderer);
## Converting a transformed path to a curve
path = agg.path_storage()
path.move_to(0,0)
path.curve3(1,0)
path.curve3(1,1)
path.curve3(0,1)
path.close_polygon()
rotation = agg.trans_affine_rotation(pi/4)
scaling = agg.trans_affine_scaling(30,30)
translation = agg.trans_affine_translation(300,250)
trans = rotation*scaling*translation
transpath = agg.conv_transform_path(path, trans)
curvetrans = agg.conv_curve_trans(transpath)
stroke = agg.conv_stroke_curvetrans(curvetrans)
stroke.width(2.0)
rasterizer.add_path(stroke)
renderer.color_rgba8( white )
agg.render_scanlines_rgba(rasterizer, scanline, renderer);
## Display it with PIL
s = buffer.to_string()
print len(s)
import Image
im = Image.fromstring( "RGBA", (width, height), s)
im.show()