Missing faces on Nvidia Curie (Geforce 6000/7000) running with Nvidia 304 driver and ATI R300 ones (regression)

[illwieckz]

Only Nvidia Curie (Geforce 6000/7000) running with Nvidia 304 driver are affected, that's a regression.

This bug is a combination of two:

• Bad normal map channel detection, seems to be related to missing ARB_texture_compression_rgtc #375 Bad normal map channel detection, seems to be related to missing ARB_texture_compression_rgtc
• a mistake introduced in Do not build GLSL shaders for disabled features #356 Do not build GLSL shaders for disabled features especially in c5c18ce do not build unused GLSL shader macro permutation.

The bug makes face disappear or being badly rendered.

Unvanquished 0.51:

Unvanquished 0.52:

[illwieckz]

The bug is caused by this:

Daemon/src/engine/renderer/gl_shader.cpp

Lines 1085 to 1089 in f1b25a8

	else if ( strcmp( token, "USE_HEIGHTMAP_IN_NORMALMAP" ) == 0 && r_reliefMapping->integer == 0 && r_normalMapping->integer == 0 )
	{
	program->unusedPermutation = true;
	return;
	}

If a normal map is detected to embed an height map in alpha channel (wrongly or not, see #375 for a case of wrong detection), and at the same time both normal and relief mapping are disabled, the whole shader permutation is disabled because it has to be disabled (both normal and relief mapping are disabled so there is no need for those operations), but that will be the shader permutation that will be used because of the unused but detected height map in alpha channel.

The bug was verified on Nvidia Geforce 6150LE, 6600 Silencer, 7500LE using Nvidia 304 driver.

An easy fix is to clear the shader boolean telling the normal map embeds an height map if there is no possible usage of that normal map file at all (because both normal and relief mapping are disabled).

Here is the result of such fix on the Geforce 6600 Silencer (it was also verified to fix the issue on other affected cards):

[illwieckz]

It's possible to reproduce the bug on any Mesa driver this way:

MESA_EXTENSION_OVERRIDE=-GL_ARB_texture_compression_rgtc ./daemon

given the engine is compiled from 0.52.0/sync branch and lowest preset is applied.

[illwieckz]

It is confirmed ATI R300 cards are affected too, with exact same artifacts.

Also, modern AMD GPU (GCN) with explicitely disabled RGTC extension on Mesa side was displaying the exact same artifacts, making the bug easy to reproduce even without requiring access to the hardware. I ❤️ Mesa.

PR #377 is known to fix the issue on all known affected hardware.

[illwieckz]

Fixed twice by #385 and #377.