rendergl: Check for GL 4.6 anisotropic TF extension

OpenGL 4.6 has brought an extension for anisotropic filtering that can work
alongside our existing GL_EXT_texture_filter_anisotropic code: check for
this new extension and, if supported, make use of it.

Link: https://registry.khronos.org/OpenGL/extensions/ARB/ARB_texture_filter_anisotropic.txt

src/engine/engine.h

@@ -206,8 +206,8 @@ static inline bool pvsoccluded(const ivec &bborigin, int size)
 }
 
 // rendergl
-extern bool hasVAO, hasFBO, hasAFBO, hasDS, hasTF, hasTRG, hasTSW, hasS3TC, hasFXT1, hasLATC, hasRGTC, hasAF, hasFBB, hasUBO, hasMBR;
-extern int glversion, glslversion, glcompat;
+extern bool hasVAO, hasFBO, hasAFBO, hasDS, hasTF, hasTRG, hasTSW, hasS3TC, hasFXT1, hasLATC, hasRGTC, hasFBB, hasUBO, hasMBR;
+extern int glversion, glslversion, glcompat, hasAF;
 extern char *gfxvendor, *gfxrenderer, *gfxversion;
 
 enum { DRAWTEX_NONE = 0, DRAWTEX_ENVMAP, DRAWTEX_MINIMAP, DRAWTEX_MODELPREVIEW };

src/engine/rendergl.cpp

@@ -1,7 +1,8 @@
 // rendergl.cpp: core opengl rendering stuff
 #include "engine.h"
 
-bool hasVAO = false, hasFBO = false, hasAFBO = false, hasDS = false, hasTF = false, hasTRG = false, hasTSW = false, hasS3TC = false, hasFXT1 = false, hasLATC = false, hasRGTC = false, hasAF = false, hasFBB = false, hasUBO = false, hasMBR = false;
+bool hasVAO = false, hasFBO = false, hasAFBO = false, hasDS = false, hasTF = false, hasTRG = false, hasTSW = false, hasS3TC = false, hasFXT1 = false, hasLATC = false, hasRGTC = false, hasFBB = false, hasUBO = false, hasMBR = false;
+int hasAF = 0;
 
 VAR(IDF_READONLY, glversion, 1, 0, 0);
 VAR(IDF_READONLY, glslversion, 1, 0, 0);
@@ -562,13 +563,21 @@ void gl_checkextensions()
         if(glversion < 300 && dbgexts) conoutf("\frUsing GL_ARB_texture_compression_rgtc extension.");
     }
 
-    if(hasext("GL_EXT_texture_filter_anisotropic"))
-    {
+    if ((glversion >= 460 || hasext("GL_ARB_texture_filter_anisotropic")) ||
+                             hasext("GL_EXT_texture_filter_anisotropic")) {
         GLint val;
-        glGetIntegerv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &val);
+
+        if (hasext("GL_ARB_texture_filter_anisotropic")) {
+            glGetIntegerv(GL_MAX_TEXTURE_MAX_ANISOTROPY, &val);
+            hasAF = 1;
+        } else {
+            glGetIntegerv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &val);
+            hasAF = 2;
+        }
+
         hwmaxanisotropy = val;
-        hasAF = true;
-        if(dbgexts) conoutf("\frUsing GL_EXT_texture_filter_anisotropic extension.");
+        if (dbgexts)
+            conoutf("\frUsing GL_*_texture_filter_anisotropic extension.");
     }
 
     if(glversion >= 300 || hasext("GL_EXT_gpu_shader4"))

src/engine/texture.cpp

@@ -784,7 +784,12 @@ void setuptexparameters(int tnum, void *pixels, int clamp, int filter, GLenum fo
     glBindTexture(target, tnum);
     glTexParameteri(target, GL_TEXTURE_WRAP_S, clamp&1 ? GL_CLAMP_TO_EDGE : (clamp&0x100 ? GL_MIRRORED_REPEAT : GL_REPEAT));
     if(target!=GL_TEXTURE_1D) glTexParameteri(target, GL_TEXTURE_WRAP_T, clamp&2 ? GL_CLAMP_TO_EDGE : (clamp&0x200 ? GL_MIRRORED_REPEAT : GL_REPEAT));
-    if(target==GL_TEXTURE_2D && hasAF && min(anisotropy, hwmaxanisotropy) > 0 && filter > 1) glTexParameteri(target, GL_TEXTURE_MAX_ANISOTROPY_EXT, min(anisotropy, hwmaxanisotropy));
+    if (target == GL_TEXTURE_2D && min(anisotropy, hwmaxanisotropy) > 0 && filter > 1) {
+        if (hasAF == 1)
+            glTexParameteri(target, GL_TEXTURE_MAX_ANISOTROPY, min(anisotropy, hwmaxanisotropy));
+        else if (hasAF == 2)
+            glTexParameteri(target, GL_TEXTURE_MAX_ANISOTROPY_EXT, min(anisotropy, hwmaxanisotropy));
+    }
     glTexParameteri(target, GL_TEXTURE_MAG_FILTER, filter && bilinear ? GL_LINEAR : GL_NEAREST);
     glTexParameteri(target, GL_TEXTURE_MIN_FILTER,
         filter > 1 ?