nv2a: Implement texture LOD bias

Fixes #767

Author: abaire

hw/xbox/nv2a/pgraph/gl/renderer.h

@@ -80,6 +80,7 @@ typedef struct TextureBinding {
     bool border_color_set;
     GLenum gl_target;
     GLuint gl_texture;
+    uint32_t lod_bias;
 } TextureBinding;
 
 typedef struct ShaderModuleCacheKey {

hw/xbox/nv2a/pgraph/gl/texture.c

@@ -120,6 +120,8 @@ static void apply_texture_parameters(TextureBinding *binding,
     unsigned int addru = GET_MASK(address, NV_PGRAPH_TEXADDRESS0_ADDRU);
     unsigned int addrv = GET_MASK(address, NV_PGRAPH_TEXADDRESS0_ADDRV);
     unsigned int addrp = GET_MASK(address, NV_PGRAPH_TEXADDRESS0_ADDRP);
+    unsigned int lod_bias =
+        GET_MASK(filter, NV_PGRAPH_TEXFILTER0_MIPMAP_LOD_BIAS);
 
     if (f->linear) {
         /* somtimes games try to set mipmap min filters on linear textures.
@@ -146,6 +148,15 @@ static void apply_texture_parameters(TextureBinding *binding,
                         pgraph_texture_mag_filter_gl_map[mag_filter]);
         binding->mag_filter = mag_filter;
     }
+    if (lod_bias != binding->lod_bias) {
+        binding->lod_bias = lod_bias;
+        int sign_extended_bias = lod_bias;
+        if (lod_bias & (1 << 12)) {
+            sign_extended_bias |= ~NV_PGRAPH_TEXFILTER0_MIPMAP_LOD_BIAS;
+        }
+        float gl_bias = (float)sign_extended_bias / 256.f;
+        glTexParameterf(binding->gl_target, GL_TEXTURE_LOD_BIAS, gl_bias);
+    }
 
     /* Texture wrapping */
     assert(addru < ARRAY_SIZE(pgraph_texture_addr_gl_map));