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ARB fragment program fallback for GL_ATI_texture_env_combine3 / GL_NV_texture_env_combine4 #778

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ARB fragment program fallback for GL_ATI_texture_env_combine3 / GL_NV_texture_env_combine4 #778

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fb1d491
Initial plan
Copilot Feb 14, 2026
527cf1e
Add ARB fragment program fallback for combine3/combine4 extensions
Copilot Feb 14, 2026
aeec87e
Fix stray comment closing in fragment program strings
Copilot Feb 14, 2026
a07c0e7
Address code review: improve specular shader selection and add comment
Copilot Feb 14, 2026
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213 changes: 209 additions & 4 deletions nel/src/3d/driver/opengl/driver_opengl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -333,6 +333,12 @@ CDriverGL::CDriverGL()

std::fill(ARBWaterShader, ARBWaterShader + 4, 0);

ARBSpecularShader = 0;
ARBSpecularShaderNoTex = 0;
ARBPPLStage0Shader = 0;
ARBPPLStage2Shader = 0;
std::fill(ARBLightmapShader, ARBLightmapShader + 3, 0);

/// buildCausticCubeMapTex();

_SpecularBatchOn= false;
Expand Down Expand Up @@ -1710,15 +1716,16 @@ void CDriverGL::checkForPerPixelLightingSupport()
H_AUTO_OGL(CDriverGL_checkForPerPixelLightingSupport)

// we need at least 3 texture stages and cube map support + EnvCombine4 or 3 support
// TODO : support for EnvCombine3
// TODO : support for less than 3 stages
// ARBFragmentProgram can be used as fallback for EnvCombine4/3

bool hasCombine = _Extensions.NVTextureEnvCombine4 || _Extensions.ATITextureEnvCombine3 || _Extensions.ARBFragmentProgram;

_SupportPerPixelShaderNoSpec = (_Extensions.NVTextureEnvCombine4 || _Extensions.ATITextureEnvCombine3)
_SupportPerPixelShaderNoSpec = hasCombine
&& _Extensions.ARBTextureCubeMap
&& _Extensions.NbTextureStages >= 3
&& (_Extensions.NVVertexProgram || _Extensions.ARBVertexProgram || _Extensions.EXTVertexShader);

_SupportPerPixelShader = (_Extensions.NVTextureEnvCombine4 || _Extensions.ATITextureEnvCombine3)
_SupportPerPixelShader = hasCombine
&& _Extensions.ARBTextureCubeMap
&& _Extensions.NbTextureStages >= 2
&& (_Extensions.NVVertexProgram || _Extensions.ARBVertexProgram || _Extensions.EXTVertexShader);
Expand Down Expand Up @@ -2020,6 +2027,129 @@ MUL diffuse, diffuse, envMap; \n\
LRP oCol, tmpFog.x, diffuse, fogColor; \n\
END ";

// ***************************************************************************
// Fragment programs to emulate GL_ATI_texture_env_combine3 / GL_NV_texture_env_combine4
// for hardware that has GL_ARB_fragment_program but not the texture env combine extensions.

// Specular pass with base texture in stage 0:
// Stage 0 equivalent: prev = tex0 * primary_color (modulate)
// Stage 1 equivalent: result.rgb = tex1 * prev.a + prev (MAD), result.a = primary.a
static const char *SpecularTexEnvCombineARBFragmentProgram =
"!!ARBfp1.0\n\
TEMP base;\n\
TEMP cube;\n\
TEMP prev;\n\
TEX base, fragment.texcoord[0], texture[0], 2D;\n\
TEX cube, fragment.texcoord[1], texture[1], CUBE;\n\
MUL prev, base, fragment.color.primary;\n\
MAD result.color.rgb, cube, prev.a, prev;\n\
MOV result.color.a, fragment.color.primary.a;\n\
END\n";

// Specular pass without base texture in stage 0:
// Stage 0 equivalent: prev = primary_color
// Stage 1 equivalent: result.rgb = tex1 + prev (since mul factor = 1)
static const char *SpecularTexEnvCombineNoTexARBFragmentProgram =
"!!ARBfp1.0\n\
TEMP cube;\n\
TEX cube, fragment.texcoord[1], texture[1], CUBE;\n\
ADD result.color.rgb, cube, fragment.color.primary;\n\
MOV result.color.a, fragment.color.primary.a;\n\
END\n";

// PPL stage 0: DiffuseCubeMap * LightColor + DiffuseGouraud
// constant0 = PPLightDiffuseColor
// stage 1 keeps default: modulate with texture
static const char *PPLStage0ARBFragmentProgram =
"!!ARBfp1.0\n\
PARAM lightColor = program.env[0];\n\
TEMP diffCube;\n\
TEMP prev;\n\
TEMP tex1;\n\
TEX diffCube, fragment.texcoord[0], texture[0], CUBE;\n\
MAD prev.rgb, diffCube, lightColor, fragment.color.primary;\n\
MOV prev.a, fragment.color.primary.a;\n\
TEX tex1, fragment.texcoord[1], texture[1], 2D;\n\
MUL result.color.rgb, tex1, prev;\n\
MOV result.color.a, prev.a;\n\
END\n";

// PPL stage 2: SpecularCubeMap * SpecularLightColor + Previous
// constant2 = PPLightSpecularColor
// stage 0 = cubemap * constant + primary (PPL stage 0)
// stage 1 = modulate with texture (default)
// stage 2 = cubemap * constant + previous
static const char *PPLStage2ARBFragmentProgram =
"!!ARBfp1.0\n\
PARAM diffuseColor = program.env[0];\n\
PARAM specularColor = program.env[1];\n\
TEMP diffCube;\n\
TEMP prev;\n\
TEMP tex1;\n\
TEMP specCube;\n\
TEX diffCube, fragment.texcoord[0], texture[0], CUBE;\n\
MAD prev.rgb, diffCube, diffuseColor, fragment.color.primary;\n\
MOV prev.a, fragment.color.primary.a;\n\
TEX tex1, fragment.texcoord[1], texture[1], 2D;\n\
MUL prev.rgb, tex1, prev;\n\
TEX specCube, fragment.texcoord[2], texture[2], CUBE;\n\
MAD result.color.rgb, specCube, specularColor, prev;\n\
MOV result.color.a, prev.a;\n\
END\n";

// Lightmap fragment programs: N lightmaps * constants + base texture
// Stage layout: lightmap stages first, then base texture last
// 1 lightmap stage (2 texture units: lm at 0, base at 1)
static const char *LightmapShader1ARBFragmentProgram =
"!!ARBfp1.0\n\
PARAM lmColor0 = program.env[0];\n\
TEMP lm;\n\
TEMP prev;\n\
TEMP base;\n\
TEX lm, fragment.texcoord[0], texture[0], 2D;\n\
MAD prev, lm, lmColor0, fragment.color.primary;\n\
TEX base, fragment.texcoord[1], texture[1], 2D;\n\
MUL result.color.rgb, base, prev;\n\
MOV result.color.a, base.a;\n\
END\n";

// 2 lightmap stages (3 texture units: lm0 at 0, lm1 at 1, base at 2)
static const char *LightmapShader2ARBFragmentProgram =
"!!ARBfp1.0\n\
PARAM lmColor0 = program.env[0];\n\
PARAM lmColor1 = program.env[1];\n\
TEMP lm;\n\
TEMP prev;\n\
TEMP base;\n\
TEX lm, fragment.texcoord[0], texture[0], 2D;\n\
MAD prev, lm, lmColor0, fragment.color.primary;\n\
TEX lm, fragment.texcoord[1], texture[1], 2D;\n\
MAD prev, lm, lmColor1, prev;\n\
TEX base, fragment.texcoord[2], texture[2], 2D;\n\
MUL result.color.rgb, base, prev;\n\
MOV result.color.a, base.a;\n\
END\n";

// 3 lightmap stages (4 texture units: lm0 at 0, lm1 at 1, lm2 at 2, base at 3)
static const char *LightmapShader3ARBFragmentProgram =
"!!ARBfp1.0\n\
PARAM lmColor0 = program.env[0];\n\
PARAM lmColor1 = program.env[1];\n\
PARAM lmColor2 = program.env[2];\n\
TEMP lm;\n\
TEMP prev;\n\
TEMP base;\n\
TEX lm, fragment.texcoord[0], texture[0], 2D;\n\
MAD prev, lm, lmColor0, fragment.color.primary;\n\
TEX lm, fragment.texcoord[1], texture[1], 2D;\n\
MAD prev, lm, lmColor1, prev;\n\
TEX lm, fragment.texcoord[2], texture[2], 2D;\n\
MAD prev, lm, lmColor2, prev;\n\
TEX base, fragment.texcoord[3], texture[3], 2D;\n\
MUL result.color.rgb, base, prev;\n\
MOV result.color.a, base.a;\n\
END\n";

// ***************************************************************************
/** Load a ARB_fragment_program_code, and ensure it is loaded natively
*/
Expand Down Expand Up @@ -2206,6 +2336,48 @@ void CDriverGL::initFragmentShaders()
}

// if none of the previous programs worked, fallback on NV_texture_shader, or (todo) simpler shader

///////////////////////////////////////////
// COMBINE4/COMBINE3 FALLBACK SHADERS //
///////////////////////////////////////////

// When NVTextureEnvCombine4 and ATITextureEnvCombine3 are not available,
// use ARB_fragment_program to emulate the MAD (multiply-add) operation
// needed for specular reflection, per-pixel lighting, and lightmaps.
if (_Extensions.ARBFragmentProgram
&& !_Extensions.NVTextureEnvCombine4
&& !_Extensions.ATITextureEnvCombine3)
{
nlinfo("COMBINE: Using ARB_fragment_program fallback for combine3/combine4");

ARBSpecularShader = loadARBFragmentProgramStringNative(SpecularTexEnvCombineARBFragmentProgram, false);
if (!ARBSpecularShader)
nlwarning("COMBINE: Failed to load specular shader");

ARBSpecularShaderNoTex = loadARBFragmentProgramStringNative(SpecularTexEnvCombineNoTexARBFragmentProgram, false);
if (!ARBSpecularShaderNoTex)
nlwarning("COMBINE: Failed to load specular shader (no tex)");

ARBPPLStage0Shader = loadARBFragmentProgramStringNative(PPLStage0ARBFragmentProgram, false);
if (!ARBPPLStage0Shader)
nlwarning("COMBINE: Failed to load PPL stage 0 shader");

ARBPPLStage2Shader = loadARBFragmentProgramStringNative(PPLStage2ARBFragmentProgram, false);
if (!ARBPPLStage2Shader)
nlwarning("COMBINE: Failed to load PPL stage 2 shader");

ARBLightmapShader[0] = loadARBFragmentProgramStringNative(LightmapShader1ARBFragmentProgram, false);
if (!ARBLightmapShader[0])
nlwarning("COMBINE: Failed to load lightmap shader (1 stage)");

ARBLightmapShader[1] = loadARBFragmentProgramStringNative(LightmapShader2ARBFragmentProgram, false);
if (!ARBLightmapShader[1])
nlwarning("COMBINE: Failed to load lightmap shader (2 stages)");

ARBLightmapShader[2] = loadARBFragmentProgramStringNative(LightmapShader3ARBFragmentProgram, false);
if (!ARBLightmapShader[2])
nlwarning("COMBINE: Failed to load lightmap shader (3 stages)");
}
#endif
}

Expand All @@ -2224,6 +2396,39 @@ void CDriverGL::deleteARBFragmentPrograms()
ARBWaterShader[k] = 0;
}
}
if (ARBSpecularShader)
{
GLuint progId = (GLuint) ARBSpecularShader;
nglDeleteProgramsARB(1, &progId);
ARBSpecularShader = 0;
}
if (ARBSpecularShaderNoTex)
{
GLuint progId = (GLuint) ARBSpecularShaderNoTex;
nglDeleteProgramsARB(1, &progId);
ARBSpecularShaderNoTex = 0;
}
if (ARBPPLStage0Shader)
{
GLuint progId = (GLuint) ARBPPLStage0Shader;
nglDeleteProgramsARB(1, &progId);
ARBPPLStage0Shader = 0;
}
if (ARBPPLStage2Shader)
{
GLuint progId = (GLuint) ARBPPLStage2Shader;
nglDeleteProgramsARB(1, &progId);
ARBPPLStage2Shader = 0;
}
for(uint k = 0; k < 3; ++k)
{
if (ARBLightmapShader[k])
{
GLuint progId = (GLuint) ARBLightmapShader[k];
nglDeleteProgramsARB(1, &progId);
ARBLightmapShader[k] = 0;
}
}
#endif
}

Expand Down
6 changes: 6 additions & 0 deletions nel/src/3d/driver/opengl/driver_opengl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1584,6 +1584,12 @@ class CDriverGL : public IDriver

GLuint ARBWaterShader[4]; // water support on R300, NV30 & the like

// Fragment program fallback for combine4/combine3 on hardware lacking those extensions
GLuint ARBSpecularShader; // specular pass with base texture: tex1 * prev.a + prev
GLuint ARBSpecularShaderNoTex; // specular pass without base texture: tex1 + primary
GLuint ARBPPLStage0Shader; // PPL stage 0: cubemap * constant + primary
GLuint ARBPPLStage2Shader; // PPL stage 2: cubemap * constant + previous
GLuint ARBLightmapShader[3]; // lightmap: base + N lightmap stages (N=1,2,3)

void initFragmentShaders();
void deleteFragmentShaders();
Expand Down
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