Quad Texture怪异行为OpenGL旧GPU

Question

I'm programming a Pascal project (using Lazarus) for school and I experienced some weird behaviour when the project was executed on one of the school computers.

It ran completely fine on my laptop from 2011 with an NVidia 650M. The school computers drivers are outdated, so it falls back to Windows GDI, which basically is a software implementation for OpenGL 1.1. So maybe the graphics card is not the cause of the problem.

Also it may be important to mention that this ONLY happens when using the GL_NEAREST method for both mag and min filters. The problem doesn't occurr when using GL_LINEAR for MAG and GL_NEAREST for MIN for example.

This is the code that loads the texture(s):

tex := LoadTGA(filename);
if tex.iType = 2 then
begin
  glGenTextures(1, @(Result.textureID));
  glBindTexture(GL_TEXTURE_2D, Result.textureID);

  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

  if tex.bpp = 3 then glFormat := GL_BGR
  else glFormat := GL_BGRA;

  glTexImage2D(GL_TEXTURE_2D, 0, tex.bpp, tex.w, tex.h, 0, glFormat, GL_UNSIGNED_BYTE, tex.data);

  FreeMem(tex.data);
end;

This is the code that renders the quad:

glColor3ub(255, 255, 255);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, q.surface.textureID);
glBegin(GL_QUADS);
  glTexCoord2f(0, 1); glVertex3f(q.points[0].x, q.points[0].y, q.points[0].z);
  glTexCoord2f(1, 1); glVertex3f(q.points[1].x, q.points[1].y, q.points[1].z);
  glTexCoord2f(1, 0); glVertex3f(q.points[2].x, q.points[2].y, q.points[2].z);
  glTexCoord2f(0, 0); glVertex3f(q.points[3].x, q.points[3].y, q.points[3].z);
glEnd;
glDisable(GL_TEXTURE_2D);

The texture has the format 32x32 pixels.

Update: As it turns out, colored quads experience a similiar bug as well. In the pic with the colored quads, it seems like GDI is doing clipping first and THEN applying the color. Should be the other way around. Now we just have to find out why. I painted the edges of the clipping triangles in the lower picture, et voila, you can see exactly where the texture is "inconsistent"

Pictures:

Answer 1

It is very hard to guess. The problem is probably related to difference in texture interpolation implemented in Nvidia and ATI drivers. Using GL_LINEAR you use different interpolation method and the "seam" is not visible. Some ideas:

• Try filling quad with solid color, eg yellow, and check if separate triangles are also visible then.
• Create your quad using two triangles (6 vertices) not GL_QUADS .
• Do you pass vertices in counter clockwise order?