Code:

---

#include <d3d9.h>
#include <stdio.h>

void export_obj(ENTITY *entity, var scale)
{
	STRING* name = str_create("#256");
	STRING* objname = str_create("#256");
	STRING* mtlname = str_create("#256");
	str_for_entfile(name, entity);
	str_trunc(name, 4);
	str_lwr(name);
	str_cpy(objname, name);
	str_cpy(mtlname, name);
	str_cat(objname, ".obj");
	str_cat(mtlname, ".mtl");
	
	int numskins = ent_skins(entity);
	int i;
	
	FILE *file = fopen(mtlname->chars, "w");
			
		for(i = 0; i < numskins; i++)
		{
			fprintf(file, "newmtl material%d\n", i);
			BMAP *b = bmap_for_entity(entity, i + 1);
			if(b)
			{
				char s[80];
				sprintf(s, "%s%d.bmp", name->chars, i);
				bmap_save(b, s);
				fprintf(file, "map_Kd %s\n", s);
			}
			fprintf(file, "\n");
		}
		
	fclose(file);



	LPD3DXMESH mesh = (LPD3DXMESH)ent_getmesh(entity, 0, 0);
	int numvertices = mesh->GetNumVertices();
	int numfaces = mesh->GetNumFaces();

	FILE *file = fopen(objname->chars, "w");
		
		fprintf(file, "mtllib %s\n", mtlname->chars);
		fprintf(file, "o %s\n", name->chars);
		
		D3DVERTEX *vb; mesh->LockVertexBuffer(0, (void**)&vb);
		WORD *ib; mesh->LockIndexBuffer(0, (void**)&ib);
		DWORD *ab; mesh->LockAttributeBuffer(0, &ab);
		
		for(i = 0; i < numvertices; i++)
			fprintf(file, "v %f %f %f\n",
				-(double)(vb[i].x * scale), (double)(vb[i].y * scale), (double)(vb[i].z * scale));
		
		for(i = 0; i < numvertices; i++)
			fprintf(file, "vt %f %f\n", (double)vb[i].u1, 1 - (double)vb[i].v1);
		
		for(i = 0; i < numvertices; i++)
			fprintf(file, "vn %f %f %f\n", -(double)vb[i].nx, (double)vb[i].ny, (double)vb[i].nz);
		
		fprintf(file, "s on\n");
		
		int material, a, b, c;
		int previousmaterial = -999;
		for(i = 0; i < numfaces; i++)
		{
			material = ab[i];
			if(material != previousmaterial)
				fprintf(file, "usemtl material%d\n", material);
			previousmaterial = material;
			
			a = ib[i*3+2] + 1;
			b = ib[i*3+1] + 1;
			c = ib[i*3+0] + 1;
			fprintf(file, "f %d/%d/%d %d/%d/%d %d/%d/%d\n", a, a, a, b, b, b, c, c, c);
		}
		
		mesh->UnlockVertexBuffer();
		mesh->UnlockIndexBuffer();
		mesh->UnlockAttributeBuffer();
		
	fclose(file);
	
	str_remove(name);
	str_remove(objname);
	str_remove(mtlname);
}

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a simple obj exporter. it writes out the mesh buffers directly so there will be hard edges at uv-borders if your modeling application recalculates the normals. the exporter could solve this by building an optimized mesh (and by supporting smoothing groups) but it would be a lot more work. in your modeling application you just would have to weld the split vertices at those borders anyway.