example-08-update: Scan through the LODs of the textures with shader.

[mcourteaux]

I have not committed the binary shaders because when I rebuild them, literally all shaders gets modified, which is not on-topic for this PR, so I'll leave that to @bkaradzic.

I also updated the positions a little bit to reduce overlap:

So this PR uses time to loop through the different LODs.

This immediately reveals some issues:

Vulkan:

bgfx_update_vk.small.mp4

OpenGL:

bgfx_update_gl.small.mp4

ETC1 is flickering badly in deeper LODs.

[bkaradzic]

It looks like that flickering is coming from border color state...

[bkaradzic]

See here:

bgfx/examples/08-update/update.cpp

Line 275 in 9547e79

m_textures[ 3] = loadTexture("textures/texture_compression_etc1.ktx", BGFX_SAMPLER_U_BORDER | BGFX_SAMPLER_V_BORDER | BGFX_SAMPLER_BORDER_COLOR(1));

ETC1 is just used to demonstrate sampler UV mode BORDER.

[bkaradzic]

Not a bug.

[mcourteaux]

Even if it's not a bug, it's crucial to assess whichever solution we come up with for #3311. My first-idea fix produces glitches for the smallest LODs. So being able to check what the LOD mipmap chain looks like for these compressed texture formats is important if we want to get it right and fix #3311.