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sprite_hound

OpenGL [solved] .obj loader weirdness

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I finally got around to doing some more work on my .obj file loader, and came across a problem I failed to solve last time. This screenshot illustrates it quite well: As you can see, it looks like some of the faces are being drawn transparent, or not drawn, and others are being drawn on top of ones they should be behind (or something). I have no idea what's causing this. Turning off lighting causes all the faces to be drawn as I'd expect (shadeless colour), so it might be something to do with that, but I don't know what. Here's the drawing code I'm using (creating display lists, these are then called when necessary):

// Goes through the vertices with that no. of verts, and draws them.
void cObjModel::createListFace(vector<cObject>::iterator j, vector<cMaterial>::iterator &m, 
		vector<int>::size_type &k, string &mName, unsigned int vertno, bool transp) {
	// While still in range, and we have that no. of verts.
	while (k != j->face.size() && j->face[k].vertex.size() == vertno) {
		// If we have the right material carry on and draw it.
		if (mName == j->face[k].material) {
			// Make sure this is the right list for it.
			if (transp && m->dissolve == 1.f || !transp && m->dissolve != 1.f) {
				++k;
				continue;
			}
			// Draw the face, with texture coords if it has a texture.
			for (vector<int>::size_type l = 0; l != vertno; ++l) {
				if (m->texture) {
					glTexCoord2f(texCoord[j->face[k].texCoord[l]].u(),
						texCoord[j->face[k].texCoord[l]].v());
				}
				glNormal3f(normal[j->face[k].normal[l]].x(),
					normal[j->face[k].normal[l]].y(),
					normal[j->face[k].normal[l]].z());
				glVertex3f(vertex[j->face[k].vertex[l]].x(),
					vertex[j->face[k].vertex[l]].y(),
					vertex[j->face[k].vertex[l]].z());
			}
			++k;
		// We need to find the right material.
		} else {
			mName = j->face[k].material;
			// Set m to point to the right material.
			for (m = material.begin(); m != material.end(); ++m) {
				if (m->name == mName) {
					break;
				}
			}
			// N.B. At the moment no colour blending with texture...
			// If we have a texture, set it.
			if (m->texture) {
				glBindTexture(GL_TEXTURE_2D, m->texture);
			// Set the new material parameters.
			} else {
				//float Ka[] = {m->refAmbient.r(), m->refAmbient.g(), m->refAmbient.b(), m->dissolve};
				float Kd[] = {m->refDiffuse.r(), m->refDiffuse.g(), m->refDiffuse.b(), m->dissolve};
				float Ks[] = {m->refSpecular.r(), m->refSpecular.g(), m->refSpecular.b(), m->dissolve};
				glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, Kd);
				glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, Kd);
				glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, Ks);
				glMaterialfv(GL_FRONT_AND_BACK, GL_SHININESS, &(m->specExp));
			}
		}
	}
}

// It would be easier here to just use multiple calls to glBegin(GL_POLYGON), but
// apparently that's pretty costly, and shouldn't be done, so we do the whole
// sorting thing instead. :-/
void cObjModel::createList() {
	// Sorts faces by number of vertices, then by material.
	for (vector<cObject>::iterator j = object.begin(); j != object.end(); ++j) {
		sort(j->face.begin(), j->face.end());
	}
	
	// Set up the list for opaque surfaces.
	opaqueListID = glGenLists(2);
	glNewList(opaqueListID, GL_COMPILE);
		for (vector<cObject>::iterator j = object.begin(); j != object.end(); ++j) {
			vector<int>::size_type k = 0;
			string mName = "";
			vector<cMaterial>::iterator m = material.begin();
			glBegin(GL_TRIANGLES);
				createListFace(j, m, k, mName, 3, 0);
			glEnd();
			glBegin(GL_QUADS);
				createListFace(j, m, k, mName, 4, 0);
			glEnd();
		}
	glEndList();
	
	// Set up the list for transparent surfaces
	transpListID = opaqueListID + 1;
	glNewList(transpListID, GL_COMPILE);
		glEnable(GL_BLEND);
		glDepthMask(GL_FALSE);
		for (vector<cObject>::iterator j = object.begin(); j != object.end(); ++j) {
			vector<int>::size_type k = 0;
			string mName = "";
			vector<cMaterial>::iterator m = material.begin();
			glBegin(GL_TRIANGLES);
				createListFace(j, m, k, mName, 3, 1);
			glEnd();
			glBegin(GL_QUADS);
				createListFace(j, m, k, mName, 4, 1);
			glEnd();
		}
		glDepthMask(GL_TRUE);
		glDisable(GL_BLEND);
	glEndList();
}




And here's the OpenGL set up I'm using, in case it's something there that's going wrong:
void cApp::reshape(int sx, int sy) {
	// Set the new width / height.
	glViewport(0, 0, sx, sy);
	
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	
	// Calculate the new aspect ratio (fov and clipping planes constant).
	gluPerspective(45.f, GLfloat(sx) / GLfloat(sy), 0.f, 100.f);
	
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}

bool cApp::initOGL() {
	// Set up OGL viewport and perspective.
	reshape(S_WIDTH, S_HEIGHT);
	
	GLfloat L0Amb[] = { 0.2, 0.2, 0.2, 1 }; GLfloat L0Diff[] = { 1, 1, 1, 1 };
	GLfloat L0Spec[] = { 0.5, 0.5, 0.5, 1 }; GLfloat L0Pos[] = { 0, 5, 0, 1 };
	glLightfv(GL_LIGHT0, GL_AMBIENT, L0Amb); glLightfv(GL_LIGHT0, GL_DIFFUSE, L0Diff);
	glLightfv(GL_LIGHT0, GL_SPECULAR, L0Spec); glLightfv(GL_LIGHT0, GL_POSITION, L0Pos);
	
	glEnable(GL_LIGHT0);
	glEnable(GL_LIGHTING);
	glLightModelf(GL_LIGHT_MODEL_TWO_SIDE, GL_TRUE);
	
	glShadeModel(GL_SMOOTH);
	glColor4f(0.9,0.6,0.2,1);
	glClearColor(0,0,0,0.5);
	glClearDepth(1);
	
	glDepthFunc(GL_GEQUAL);
	glEnable(GL_DEPTH_TEST);
	
	glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
	
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glEnable(GL_TEXTURE_2D);
	
	return true;
}




If anyone can see anything that could be causing this problem it would be greatly appreciated. thanks, sprite_hound. [Edited by - sprite_hound on May 19, 2007 10:47:45 AM]

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glEnable(GL_DEPTH_TEST); ???

Okay, nevermind, I see you have that. Are the normals and winding order done properly? Is backface culling on? I don't see it in your code.

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Quote:
Original post by Vampyre_Dark
glEnable(GL_DEPTH_TEST); ???

Okay, nevermind, I see you have that. Are the normals and winding order done properly? Is backface culling on? I don't see it in your code.


Hum. Yep, glEnable(GL_CULL_FACE); seems to solve everything. *looks embarrassed*
I really should have spotted that.

Thanks. :)

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In the line:

gluPerspective(45.f, GLfloat(sx) / GLfloat(sy), 0.f, 100.f);

Make sure the near plane isn't set to 0.f or it'll cause strange things with depth testing (try 0.1f or something).

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@timstump - thanks, I've changed that too. :)

And I've hit another problem. This time with textures. The model is basically the same as in the first screenshot (from a slightly different angle), and with a texture I've applied (the same drawing code as before). As you can see quads are rendered fine, but triangles just don't seem to show up (though they show up fine without the texture):



I really don't know what I'm doing wrong here, but it's probably something simple. I'm pretty sure the information is being sent to opengl ok, so I'm not sure what's happening.

[EDIT:] Nevermind. It appears you can't put calls to glBindTexture() inside a glBegin() glEnd() section. Meh - means I'll have to rewrite this I guess. Oh well.

[Edited by - sprite_hound on May 19, 2007 10:06:22 AM]

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