On Nov 20, 3:13 pm, "Casey Duncan" <[EMAIL PROTECTED]> wrote:
> Here's one way you could do it:
>
> Grab a texture from the buffer that is the bounding box of your lasso
> selection.
> Make a lasso mask that is white only inside the selection
> draw the mask into the stencil buffer
> draw the rectangular texture you grabbed (with the stencil test on)
> into your destination buffer
The stencil buffer is just what I needed. This example makes it very
easy to understand:
http://pseudogreen.org/bzr/pyglet_superbible/ch03/stencil.py
My test code ended up looking like this (graphics lib more or less
wraps some basic pyglet/OpenGL calls):
pyglet.gl.glClearStencil(0)
pyglet.gl.glEnable(pyglet.gl.GL_STENCIL_TEST)
pyglet.gl.glClear(pyglet.gl.GL_STENCIL_BUFFER_BIT)
pyglet.gl.glStencilFunc(pyglet.gl.GL_NEVER, 0x0, 0x0)
pyglet.gl.glStencilOp(pyglet.gl.GL_INCR, pyglet.gl.GL_INCR,
pyglet.gl.GL_INCR)
graphics.set_color(1,1,1,1)
graphics.draw_rect(self.x1,self.y1,self.x2,self.y2)
graphics.set_color(0,0,0,1)
graphics.draw_ellipse(self.x1,self.y1,self.x2,self.y2)
pyglet.gl.glStencilFunc(pyglet.gl.GL_NOTEQUAL, 0x1, 0x1)
pyglet.gl.glStencilOp(pyglet.gl.GL_KEEP, pyglet.gl.GL_KEEP,
pyglet.gl.GL_KEEP)
graphics.set_color(1,1,1,1)
graphics.draw_image(self.selection, self.x1, self.y1)
pyglet.gl.glDisable(pyglet.gl.GL_STENCIL_TEST)
That code draws an oval-shaped section of the image self.selection.
On Nov 20, 3:16 pm, "Tristam MacDonald" <[EMAIL PROTECTED]> wrote:
> For a really simple approach, you can use multi-texturing with
> multiplicative blending against a mask texture. This will mask any areas
> where the mask texture is 0, and leave any areas where it is 1, but it may
> not be the most flexible approach.
I couldn't find any useful information about this method with a
rudimentary web search.
> If you are using shaders, you can use a mask texture and a pixel shader to
> render only the unmasked portion of another texture (use the discard
> instruction for masked pixels).
>
> If you aren't using shaders, you may be able to work something out with the
> stencil buffer, although this wont be as straightforward.
My OpenGL knowledge is scattered and specialized, so I'm not using
shaders. The stencil buffer method was actually very straightforward:
use boilerplate setup code, draw mask, then more boilerplate, then
draw stuff, then more boilerplate.
> C extensions are pretty much identical on OS X to linux, although you do
> need to pass the compiler a few different options. If you need help
> constructing a makefile for a C extension, I have several extension modules
> building cross-platform, so I can probably explain the process.
I tried looking for examples a few days ago but couldn't find anything
more recent than OS X 10.2, which had a much earlier version of
Python. Links to examples would be much appreciated. I'm decent with
C, but have used it primarily for homework assignments, so for now I'm
considering a C extension to be out of the scope of this project.
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