3 CHOPS - CAPTURING GEOMETRY

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Verity Wiggins
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1 3 CHOPS - CAPTURING GEOMETRY In this lesson you will work with existing channels created in CHOPs that is modified motion capture data. Because there is no capture frame in the motion capture data, one must be created. This will be done in CHOPs, and following that, you will used the capture SOP to give life to a model. Houdini Training 4.0 Side Effects Software

3.1 GETTING STARTED 1. Launch Houdini. 2. From the main edit menu select File Open. The file you want to open is called bill_cap.hip. Hit the accept button when selected to load it into Houdini.

2 3.1 GETTING STARTED 1. Launch Houdini. 2. From the main edit menu select File Open. The file you want to open is called bill_cap.hip. Hit the accept button when selected to load it into Houdini. What loads into Houdini is a what appears to be a character, but is, in fact several capture regions, that are in the form of a human. There is no ik system here, just capture regions. Also at this point you are at frame 0. This will be the capture frame. At this time you will not worry about the character you are going to capture, but you are going to deal with the animation channels that are located within the CHOPs editor. 3. From the desktop selector button located at the top of the viewport, select the CHOPs_Training desktop. You will notice in the CHOPs area of the desktop (left-side), that there is already a CHOP tile placed. This is a File CHOP which contains all of the motion capture data which will be making the character do backflips. There are a total of 57 channels which are controlling each of the capture regions. 4. Toggle on its export flag, and press play to view the animation. You will immediately notice that the channel names match, and therefore are successfully being exported up to the different objects making up the character. Having played back the sequence, you will see the character jump up and do a backflip. If you toggle on the information button of the File CHOP, you will see that the channels start at frame 1. What is significant about these CHOPs channels is that the moment you export channels from CHOPs, and override channels up in object space, it becomes impossible to capture geometry the traditional way by adding a keyframe at frame 0, and working from there. The capture frame must be done in the CHOPs editor. 5. Toggle off the export flag of the File CHOP. You should see the character return to its capture pose. 6. Place a Fetch CHOP to the Left of the File CHOP. Rename it to be capture_frame. Working with its parameters: In the OP field, change the default parameters to be obj followed by none. Refer to the image below. 58 Side Effects Software 1999 Houdini Training 4.0

3 This will allow you to enter in variables in the Channels field below the OP field. In this case you want to fetch all of the rotation channels from the various bone objects, as well as the bone_hips translation channels. In the Channels field, delete the default *, and enter the following parameters: bone_*/r? bone_hips/t? Open the Channel folder. In the Channel Range field change it to be Use Start/End. Leave the Start field at 0. Change the End field to be 0. Go to the Common folder. Change the Units type from Seconds to Frames. Toggle on the Graph flag of this CHOP. Toggle on the Lock flag of the Fetch CHOP. If you also refer to the information button of this CHOP, you should see that you have fetched 57 channels, and that the start and end frames are both at 0. It is now just a simple matter of using a Sequence CHOP to sequence these two CHOPs. 7. Append a Sequence CHOP after the capture_frame CHOP. Pipe the output of the File CHOP into the Sequence CHOP. (this is a multiinput CHOP) This CHOP will sequence in order of input the channels being fed into it, it is therefore important that the order of input is followed correctly with the capture_frame CHOP being the first input. If this is not done than it would lead to difficulty attempting to capture the geometry. 8. Change the frame counter to be at frame Toggle on the Graph and Export flags of the Sequence CHOP. You will see the character immediately snap out of his capture position. Press play to see the animation. Press stop. At this point it looks like nothing that you would have hoped for. The jump is not happening properly, and nothing seems to look correct at all. Houdini Training 4.0 Side Effects Software

Toggle on the information button of the File CHOP. Make note of the first 6 channels. They are all bone_hips/channels. Toggle on the information button of the capture_frame CHOP.

4 Toggle on the information button of the File CHOP. Make note of the first 6 channels. They are all bone_hips/channels. Toggle on the information button of the capture_frame CHOP. Make note of its first 6 channels. You will notice that the first three channels are bone_hips/channels. However, they are rotation channels, (the File CHOPs first three channels are tx ty tz), These channels are not the same, not to mention that the next three are not even bone_hips channels. The Sequence CHOP by default matches the channels in their order of input. In this case the channels do not really match at all. Return to the Sequence CHOPs parameters. Change the Match By parameter from Channel Number to by Match By Channel Name. Press play. All is well. The flip is happening properly. Return the frame counter to frame 0. It is now time to capture the geometry. so that you may see the character (and not just capture regions) jump. 10. Working in the Objects area of the desktop (right-side). There is an object called Bill_geo that is currently not being displayed. Toggle its display flag on. You will now see the character known as Bill. At frame 0 he is ready to be captured. 11. Enter into the Bill_geo SOP editor. 60 Side Effects Software 1999 Houdini Training 4.0

5 Append a Capture SOP to the Bill SOP. Toggle its Display flag on. The Capture SOP will immediately give you an error flag. In the Capture SOPs parameters, change the parent Object from none to bone_hips. Change the Point Coloring from Default Source Color to Color by Capture Region. After you change the coloring method, you will see parts of Bill turn Red. These are areas which are not being effectively captured. Important: You must make sure that you frame number matches the Capture Frame number in the Capture SOPs parameters. By default it is at 0. Bad capture areas. At this point you are going to need to take some time to modify the parameters within each of the necessary capture regions to ensure that there are no red areas. This will be done by entering in to the SOP editor of the specific area (i.e. bone_righthip) and modifying it s Cap parameters until the red disappears. Once again, make sure you are at the Capture Frame otherwise you will not see any changes. Another important fact about capturing geometry. Make sure that you try to minimize overlapping capture regions. This can lead to complications when animating. This is particularly important in areas like the underarm. This is made easier by capturing geometry by surface as opposed to capturing by points. 12. Once you have finished modifying you capture regions. Save your file. 13. Append a Deform SOP to the Capture SOP. Toggle its Display flag on. 14. Press the u key to navigate the SOPs editor up one level to Objects. Houdini Training 4.0 Side Effects Software

6 Change into List mode to view the object list. t At the top of the object list click on the name. button. This will highlight the entire list. Click on the Display flag. This turns off the display flag of everything. Turn on the Display flag of the Bill_geo object and the floor object. Press play. You will now see Bill stand on the grid crouch, leap into the air and do backflips. In this particular lesson the capture region were not attached to any bones. This was just one method of working with capture regions. One might also create the ik system for the entire skeleton, and work with the capture regions within each bone. 62 Side Effects Software 1999 Houdini Training 4.0

In this lesson we are going to create cartoon eyes and parent them to the head bone.

In this lesson we are going to create cartoon eyes and parent them to the head bone. Open up your fish project and in the modeling object window we will create a new object layer to develop the eyes, then