gx: add GX_GetTexObjFilterMode()

Without this function there is no way to retrieve the texture
minification and magnification filters.

gc/ogc/gx.h

@@ -4110,6 +4110,21 @@ u16 GX_GetTexObjWidth(const GXTexObj* obj);
  */
 void GX_GetTexObjLOD(const GXTexObj* obj, f32 *minlod, f32 *maxlod);
 
+/*!
+ * \fn void GX_GetTexObjFilterMode(const GXTexObj* obj, u8 *minfilt, u8 *magfilt)
+ * \brief Returns the filter mode for the texture object \a obj.
+ *
+ * \note Use GX_InitTexObjLOD() or GX_InitTexObjFilterMode() to initialize the
+ * texture filter mode.
+ *
+ * \param[in] obj ptr to a texture object
+ * \param[out] minfilt minification filter mode; will be one of \ref texfilter
+ * \param[out] maxfilt magnification filter mode; will be \a GX_NEAR or \a GX_LINEAR
+ *
+ * \return none
+ */
+void GX_GetTexObjFilterMode(const GXTexObj *obj, u8 *minfilt, u8 *magfilt);
+
 /*!
  * \fn void GX_GetTexObjAll(const GXTexObj* obj, void** image_ptr, u16* width, u16* height, u8* format, u8* wrap_s, u8* wrap_t, u8* mipmap);
  * \brief Returns the parameters described by a texture object. Texture objects are used to describe all the parameters associated with a texture, including size, format, wrap modes, filter modes, etc. Texture objects are initialized using either GX_InitTexObj() or, for color index format textures, GX_InitTexObjCI().

libogc/gx.c

@@ -3035,6 +3035,22 @@ void GX_GetTexObjLOD(const GXTexObj *obj, f32 *minlod, f32 *maxlod)
 	*maxlod = _SHIFTR(ptr->tex_lod, 8, 8) / 16.0f;
 }
 
+void GX_GetTexObjFilterMode(const GXTexObj *obj, u8 *minfilt, u8 *magfilt)
+{
+	const struct __gx_texobj *ptr = (const struct __gx_texobj*)obj;
+	u8 hw_filt, i;
+
+	*magfilt = ptr->tex_filt & 0x10 ? GX_LINEAR : GX_NEAR;
+	hw_filt = _SHIFTR(ptr->tex_filt, 5, 3);
+	for (i = 0; i < sizeof(_gx2HWFiltConv); i++)
+		if (_gx2HWFiltConv[i] == hw_filt) {
+			*minfilt = i;
+			break;
+		}
+	if (i == sizeof(_gx2HWFiltConv)) /* we didn't find it */
+		*minfilt = GX_NEAR;
+}
+
 void GX_GetTexObjAll(const GXTexObj *obj, void** image_ptr, u16* width, u16* height,
                      u8* format, u8* wrap_s, u8* wrap_t, u8* mipmap)
 {