ARB fragment program fallback for GL_ATI_texture_env_combine3 / GL_NV_texture_env_combine4

[Copilot]

On Intel HD graphics, neither GL_ATI_texture_env_combine3 nor GL_NV_texture_env_combine4 is available, disabling specular reflection (armor), per-pixel lighting, and multi-lightmap-per-pass rendering. GL_ARB_fragment_program is available on these GPUs and can emulate the required MAD (multiply-add) operations.

Fragment programs added (driver_opengl.cpp)

• Specular: tex1 * prev.a + prev (with base texture) and tex1 + primary (without)
• PPL stage 0: cubemap * lightColor + primary — diffuse per-pixel lighting (2 stages)
• PPL stage 2: full 3-stage PPL with diffuse + specular cube maps and light color uniforms
• Lightmap: 1/2/3 lightmap stages with per-stage factor colors via program.env params

Programs are compiled in initFragmentShaders() only when combine extensions are absent but ARBFragmentProgram is present. Cleaned up in deleteARBFragmentPrograms().

Rendering paths updated (driver_opengl_material.cpp)

• beginSpecularMultiPass() / setupSpecularPass(): single-pass specular via fragment program instead of broken 2-pass fallback (which was #ifdef'd out due to Intel texture bugs)
• setupPPLPass() / setupPPLNoSpecPass(): early-return path binds fragment program with light colors as program.env uniforms, skipping all texenv setup
• computeLightMapInfos() / setupLightMapPass(): up to 3 lightmaps per pass (previously fell back to 1)
• All end*MultiPass() functions disable GL_FRAGMENT_PROGRAM_ARB when the fallback was active

Capability detection (driver_opengl.cpp)

• checkForPerPixelLightingSupport(): ARBFragmentProgram now qualifies as combine support

Example specular fragment program:

!!ARBfp1.0
TEMP base, cube, prev;
TEX base, fragment.texcoord[0], texture[0], 2D;
TEX cube, fragment.texcoord[1], texture[1], CUBE;
MUL prev, base, fragment.color.primary;
MAD result.color.rgb, cube, prev.a, prev;
MOV result.color.a, fragment.color.primary.a;
END

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement fragment program fallback for GL_ATI_texture_env_combine3 and GL_NV_texture_env_combine4</issue_title>
<issue_description>On Intel HD graphics the GL_ATI_texture_env_combine3 and GL_NV_texture_env_combine4 extensions are not supported, this causes reflection on armor to become disabled. As GL_ARB_fragment_program is available on this graphics target, it should be possible to support the MAD operator in the texture stages by generating a fragment program.

The behaviour of GL_ATI_texture_env_combine3 is the desired ideal behaviour.</issue_description>

<agent_instructions>:)</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Implement fragment program fallback for GL_ATI_texture_env_combine3 and GL_NV_texture_env_combine4 #682

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