WOTLK terrain sometimes weirdly checkerboxed

[wgreenberg]

For example, here on Strand of the Ancients:

This might be a texture decoding issue, or maybe the heightmapped ADT terrain?

[magcius]

Improved by 6d8a82e. The crater here still seems to have a seam; up to you whether you want to keep this issue open for that, or close and open a new one.

[magcius]

    alphaBlend.r = 1.0 - saturate(dot(alphaBlend.gba, vec3(1.0)));
    vec4 tex = tex0*alphaBlend.r + tex1*alphaBlend.g + tex2*alphaBlend.b + tex3*alphaBlend.a;
    // vec4 tex = mix(mix(mix(tex0, tex1, alphaBlend.g), tex2, alphaBlend.b), tex3, alphaBlend.a);

Treating the weights as if they are weight blends like heightmap texturing does fixes Strand of the Ancients, but it breaks Alterac Valley. Screenshots attached. Strand of the Ancient's WDT doesn't appear to have the "hasHeightTexturing" flag marked, but that might just be us not parsing out the flags correctly.