Offscreen buffers don't do texturemapping at all and I haven't found
workaround yet. Example code is below:
---

PGraphics warpbuffer;

size(500, 500, P3D);
warpbuffer = createGraphics(500, 500, P3D);

PImage tmptexture = createImage(100,100,RGB);
for(int i = 0; i < tmptexture.pixels.length; i++) {
tmptexture.pixels[i] = color(random(0,255));
}

beginShape();
textureMode(NORMALIZED);
texture(tmptexture);
vertex(20, 10, 0, 0);
vertex(200, 20, 1, 0);
vertex(190, 210, 1, 1);
vertex(10, 200, 0, 1);
endShape();

warpbuffer.beginDraw();
warpbuffer.beginShape();
warpbuffer.textureMode(NORMALIZED);
warpbuffer.texture(tmptexture);
warpbuffer.vertex(20, 10, 0, 0);
warpbuffer.vertex(200, 20, 1, 0);
warpbuffer.vertex(190, 210, 1, 1);
warpbuffer.vertex(10, 200, 0, 1);
warpbuffer.endShape();
warpbuffer.endDraw();

image(warpbuffer,200,200);

this is a dupe of some other stuff, but provides a helpful example for
tracking down the issue. the problem is that the alpha channel of the
shapes that are drawn is not being set properly. you can actually add the
following to the code and it'll work:

for (int i = 0; i < warpbuffer.pixels.length; i++) {
warpbuffer.pixels[i] |= 0xFF000000;
}

this will simply set the warpbuffer to be completely opaque, and show the
image.

(In reply to comment #1)
> this will simply set the warpbuffer to be completely opaque, and show the
> image.

Ohhoh, thanks! I didn't know it was about alpha.

fixed for 0127. this should also fix a number of other problems with
createGraphics().