What would cause white lines to be drawn accross a textured quad? I have a quad and the texture appears and the vertex colors affect the color also, but then I get this (usually single) straight light at some obscure angle, in white, accross the quad. When I position the quad at different coordinates the line sometimes stays in the same orientation and sometimes shifts to a different angle. There is no rotation going on in the modelview matrix. Also the line isn't fixed to where the edge of one of the triangles would be.
Any ideas?
I ran into a possibly related issue, drawing a bunch of alphablended PNG images:
Initially, everything draws perfectly... Then if I unload every single one of my images, flushmem, etc. , change to a different screenmode and reload all images, one of them gets draws weird: the top of the image that should be alpha-blended into the background gets drawn as a straight, solid light-gray line.
(The actual sprite itself is all darkish-brown, drawn on a dark brown background. No gray present in either foreground or background. No rotation or scaling. Plain vanilla non-interlaced PNG image with alpha.)
Similar alpha gradients on the sides and bottom of the image are blended just fine.
Luckily I figured out an alternative system and I no longer need the sprite in question, but it was still a very weird issue to run into.
Dang! It sure is weird whatever it is. I wondered if it is something to do with alpha doing something odd. All I do is load an RGB PNG image and copy the red channel into the alpha channel. It has been working fine before when I uploaded only the alpha channel as a GL_ALPHA texture, but now I upload and use the whole RGBA I get these dumb lines on the screen. Blend mode is GL_ONE,GL_ONE.
[Edit] It seems that GL_ONE,GL_ONE produces the white lines, whereas GL_SRC_ALPHA,GL_ONE does not, even if the entire source alpha is 1.0.