Live Lecture Chat – January 13, 2021
09:58:10 From Jacob Eckroth(He/him/his) : For assignment 2, I’ve noticed that even when the alpha for a pixel is very low I still can’t see behind it until it gets to the discard threshold. Would you need to do a double pass to actually blend the foreground pixel and the background pixel?
This is an artifact of the way that the graphics hardware pipeline works. This is what I wanted you to see. Any use of transparency, even uAlpha=0., causes the Z-buffer to be written, which can contaminate the ability to properly display the rest of the scene, depending on the order that things are displayed in. Notice that using discard always works, where uAlpha=0. would not.
10:12:57 From Jacob Eckroth(He/him/his) : since it’s a float is it ok if we just do less than a number really close to 0?
Yes.
10:00:34 From Jacob Eckroth(He/him/his) : Also, one thing that I’ve noticed is that no matter where I rotate around the object I still see the specular even if the light is on the other side.
This is a function of whether or not you multiply the light position by the gl_ModelViewMatrix. If you do, then the light, and thus the specular highlight, moves with the object. If you don’t, the light stays in the same spot and the specular highlight doesn’t move.
10:02:40 From Raymon, Nathaniel A : are you just using the quick and dirty lighting from the project page?
Yes.
10:05:28 From Raymon, Nathaniel A : vNf should be normalize(gl_Normal); 10:05:55 From Raymon, Nathaniel A : instead of multiplying by the normalmatrix
Typically we always multiply the normal by the gl_NormalMatrix. If you don’t, then the object moves but the normals stay fixed. Since the normal are part of the object, you really want the normals to move with it.
10:14:46 From Jacob Eckroth(He/him/his) : I’ve noticed with glman we can set uniform bools and uniform floats with sliders. Are there any other things we can do like vec3s? Or are those the main options
You can also set an integer. When you use the 3-argument angle brackets, glman looks into your symbol table to see if it should create a float slider or an integer slider.
10:29:14 From Jacob Eckroth(He/him/his) : imagine the people that make graphics cards having to make it adapt to whatever monitor is attached to it
A lot of time, that it the job of the driver software, for example, turning colors in the range 0.-1. into colors in the range 0-255.
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10:44:25 From Jacob Eckroth(He/him/his) : If we want to is it possible to update the normals to be the cube normals? [in the cow morphing example]
Yes. I didn’t do that because I wanted the cow’s face to always be visible.
11:06:59 From Todankar, Diksha Pritam : is this a texture you’re using on a circle? I mean how did you color-code the stuff on the map? [in the Corvallis hyperbolic geometry example]
It is a bunch of colored lines, compliments of the Corvallis Fire Department and their .shp files.
11:10:30 From Jacob Eckroth(He/him/his) : that’s crazy. I bet bump mapping with a tiny bit of displacement looks great like on a detailed brick wall
Yes, although you can do almost as well with Normal Mapping. See the discussion of that next week!
11:11:53 From Haoyuan Qiu : do we have classes on next Monday?
Out of respect for the MLK Day events, I will hold neither 8:00 AM OHs nor the 10:00-12:00 Live Lecture on Monday January 18. Out of respect for you, I will hold 12:00-2:00 OHs. The TAs will not be holding OHs that day.
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