Topogun is a great little program for retopologising High poly Zbrush meshes into low poly meshes which can then be imported into 3D Studio Max or used in game engines. Since it is has such a narrow and specific function, it can be learned rather quickly. Here are some notes on how to use it, Including a brief section on how to render out texture maps.
These notes were made from the awesome tutorials by theEZhexagon available here:
and from Andrew Smith available here:
BASIC CONTROLS AND HOTKEYS
Mouse Wheel: Zoom in and out.
R Click: Automatically switch to the SimpleCreate Tool
F: Refocus on model
Alt + L Click: Hold to rotate around the model.
Alt + Mousewheel. Click and hold the mousewheel to pan the screen.
RETOPOLOGISING A MODEL
1: Open your hi-poly file by clicking File> Load Reference or by clicking the grey Load Ref tab just underneath the menu bar. Topogun works with .obj files. NB – To make things easier on your hardware, run a pass of Decimation Master on your ZBrush model to lower it’s poly count without losing detail.
2: Say you want to start with the leg on a human body model. Start by selecting the pencil tool from the tool bar. On the little Tool options window that appears you can set set points higher or lower depending on how many polys you want to create. Note that there’s a little checked option called ‘Line’. Leave it checked for now.
3: Click and drag a line across the leg, making sure it starts and ends on empty space. Make sure the lines are nice and perpendicular to the flow of the object. You will notice a yellow band appears on your model. Next, draw another line adjacent to the first. Keep adding lines to cover the area needing retopologised.
4: In the Tool options box, check the loft circle instead of line. Now, draw a line connecting the top ring to the bottom. Click evaluate, and a new set of polygons should appear. (If you are having trouble drawing your lines, check the ‘Steady Mouse’ button at the top. This will keep them straighter.)
5:Now click clear all to remove the pencil lines. You can also click clear last if you make a mistake while drawing. NB: You can continue to adjust the points values of every line you’ve drawn before lofting and creating the new polys.
6: If you need to select a particular set of verts, edges or faces, use the SimpleEdit’ tool along with the buttons along the bottom of the screen. These will allow you to select loops and rings, and faces from verts etc. In the tool Options box, you can now choose between vertex, edge or faces when making selections. Double Clicking on an Edge will automatically select all edges in a ring. xxxxxxxxxxx will select all edges in a loop.
7: If you want to add an extra set of edges to create new polys- say if you havent created enough loops around the legs, simply select one edge and choose the Connect Ring Button on the right side of the screen.
8: If you end up with verts or polys sticking inside or away from the reference model, simply select the verts and choose the ‘Snap to Ref’ button from the right hand side.
9: Extra: If you are merely using the ‘Simple Create’ tool to draw polys point by point onto your model, you will not automatically create faces. You must hold Ctrl and click on the 4th point to create a poly between your verts.
SYMMETRY
1. The obj file used here wasn’t symmetrical- it was all I had to hand! Apologies. However, When working on an arm or a leg of a symmetrical reference mesh, select the grey Symmetry button at the lower right of the screen to work on both limbs at the same time.
2. Select Vertex, then select all the vertexes you just created on the leg. now on the list of grey buttons on the right, choose ‘Create Sym’. This will create a duplicate set of new polys on the other leg.
3: When using symmetry on a character, you may get a seam down the mirror line of your mesh. select all of these verts and choose xxxxxxxxxxx to weld these verts together.
STITCHING PIECES TOGETHER
You will probably work on the arms, then the legs, then the torso etc in separate pieces. when it comes to joining these pieces together you can do several things.
1: When working with verts, choose the ‘SimpleEdit’ tool. Ctrl + L Click on a vertex, and drag it to the vertex you want to weld it to. When the vert turns red, release the mouse button and the two will be connected.
2: Select the ‘Bridge’ tool from the toolbar. Hovering the cursor over the model between two verts will show a red line connecting them. Left Click to add a new edge between them continue adding edges to create new polys.
SUBDIVIDING.
1: Along the top of the screen are a series of grey buttons. At any time click the SubD Button to remove the reference mesh and leave only the new polys. This will also subdivide the new polys, creating new verts that automatically cling to the reference mesh.
2: In the menu bar, choose Subdivision> Preferences to open a small window where you can set your subdivision level depending on how high or low poly you want the new mesh to be.
BAKING TEXTURE MAPS.
1: After creating your low poly mesh and saving it as a .obj file, open it in 3DS Max (or your software of choice), unwrap it and save.
2: Reopen Topogun and click the grey Load Scene button just below the Menu Bar. You will be asked to open your low poly mesh, followed by your high poly reference mesh.
3: Once both meshes have loaded, in the Menu bar choose Bake > Generate Maps. In the panel that opens, you can choose to generate normal, Displacement, colour (diffuse), andambient occlusion maps.
From here you can customise your maps: name each file and location to save to, set the map size, set sample rate (higher is better but takes longer to render) etc.
4: After choosing your settings, scroll to the bottom and click ‘Generate’. This will create all of the selected maps.