在最近邻插值OpenGL像素中心的情况下会发生什么

Question

What happens when a nearest neighbour interpolation occurs where the pixel for which the nearest neighbour interpolation is being calculated in texture is at the same distance from two neighbouring pixels, and the pixel falls equal distance in length from the two pixels that it is trying to correctly interpolate for a new pixel in the case of magnification.

Does OpenGL take the two pixels and interpolate a colour from the texture by taking an average value from the two at same length distance or something else happens?

Answer 1

The spec is very clear about how texels are selected from a texture coordinate:

Minification

Section 8.14 specifies the minification behaviour (I skip here a lot of things regarding wrap modes etc. and explain the 2D case):

Let [s(x,y), t(x,y)] be the texture coordinates at screen position (x,y). Now we define u(x,y) = s(x,y) * texture_width and v(x,y) = t(x,y) * texture_height. In case of nearest neighbor interpolation, the texel is given by the integer coordinates (i,j), where i = floor(u(x,y)) and j = floor(v(x,y)).

Lets do an example: Assuming we have a texture of size 2x1 and a lookup position of [0.5, 0.5]. In this case u(x,y) = 0.5 * 2 = 1 and v(x,y) = 0.5 * 1 = 0.5. Now we get i = floor(1) = 1 and j = floor(0.5) = 0. So, the result will be the color of the right texel.

Magnification

Section 8.15 states the the magnification behaves exactly as the minification.