Difference between revisions of "3D Fundamentals Tutorial 6"
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The tutorial video is on YouTube [https://www.youtube.com/watch?v=h_Aqol0oTs4 here]. | The tutorial video is on YouTube [https://www.youtube.com/watch?v=h_Aqol0oTs4 here]. | ||
| − | + | <div class="mw-collapsible mw-collapsed"><br /> | |
| − | * Recap of our problem: | + | * Recap of our problem: triangles are always drawn in the same order [https://youtu.be/h_Aqol0oTs4?t=0m20s 0:20] |
| + | * Solution: Back face culling [https://youtu.be/h_Aqol0oTs4?t=2m02s 2:02] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* Poor solution: painter's algoritm (sort the triangles back to front, draw front ones last) | ||
| + | :* Better solution: never draw back facing triangles. For convex single objects front facing triangles will never overlap | ||
| + | </div> | ||
| + | * Using a triangle's surface normal to determine its orientation [https://youtu.be/h_Aqol0oTs4?t=5m15s 5:15] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* Just the z-component of the face normal is not good enough | ||
| + | :* Correct approach: take the viewing vector (v1) and the face normal direction (v2) | ||
| + | :* (viewing vector: vector from focal point to any point on the triangle in world space) | ||
| + | :* If their dot product is negative (opposide directions), the triangle's face is towards the focal point | ||
| + | </div> | ||
| + | * How to find the face normal: the cross product [https://youtu.be/h_Aqol0oTs4?t=9m51s 9:51] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* Comparison of concepts of dot product and cross product | ||
| + | :* v1 x v2 yields a perpendicular vector (following left hand rule in our system) with length l = area of the parallelogram spanned by v1 and v2 | ||
| + | </div> | ||
| + | * The math equation for the cross product [https://youtu.be/h_Aqol0oTs4?t=16m13s 16:13] | ||
| + | * Getting the face normal vector of our triangles [https://youtu.be/h_Aqol0oTs4?t=19m26s 19:26] | ||
| + | * Implementing these concepts in our code [https://youtu.be/h_Aqol0oTs4?t=21m04s 21:04] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* The cross product operator in <code>Vec3</code> | ||
| + | :* Using cull flags for the triangles [https://youtu.be/h_Aqol0oTs4?t=22m32s 22:32] | ||
| + | </div> | ||
| + | * Culling needs to be performed before the transformation to screen space [https://youtu.be/h_Aqol0oTs4?t=24m33s 24:33] | ||
| + | * The order of the vertices (i.e. the index lists for triangles) matters [https://youtu.be/h_Aqol0oTs4?t=26m04s 26:04] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* Use the left handed winding rule when constructing the triangle index list [https://youtu.be/h_Aqol0oTs4?t=27m08s 27:08] | ||
| + | </div> | ||
| + | * Introduction of the base class <code>Scene.h</code> for scene definitions its derived classes [https://youtu.be/h_Aqol0oTs4?t=28m50s 28:50] | ||
| + | * Remaining issues: concave shapes, triangle intersections, occlusion [https://youtu.be/h_Aqol0oTs4?t=31m10s 31:10] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* You can't easily sort this with sorting (although sorting has its place in 3d graphics) | ||
| + | :* We will come back to these issues later in the series | ||
| + | </div> | ||
| + | </div> | ||
== Downloads == | == Downloads == | ||
Latest revision as of 23:51, 11 May 2020
Get rid of those dirty back-facers, we don't serve their kind here. Also, learn the new sex move that is taking New England by storm: the Bridgeport Shocker.
Video
The tutorial video is on YouTube here.
- Recap of our problem: triangles are always drawn in the same order 0:20
- Solution: Back face culling 2:02
- Poor solution: painter's algoritm (sort the triangles back to front, draw front ones last)
- Better solution: never draw back facing triangles. For convex single objects front facing triangles will never overlap
- Using a triangle's surface normal to determine its orientation 5:15
- Just the z-component of the face normal is not good enough
- Correct approach: take the viewing vector (v1) and the face normal direction (v2)
- (viewing vector: vector from focal point to any point on the triangle in world space)
- If their dot product is negative (opposide directions), the triangle's face is towards the focal point
- How to find the face normal: the cross product 9:51
- Comparison of concepts of dot product and cross product
- v1 x v2 yields a perpendicular vector (following left hand rule in our system) with length l = area of the parallelogram spanned by v1 and v2
- The math equation for the cross product 16:13
- Getting the face normal vector of our triangles 19:26
- Implementing these concepts in our code 21:04
- The cross product operator in
Vec3 - Using cull flags for the triangles 22:32
- The cross product operator in
- Culling needs to be performed before the transformation to screen space 24:33
- The order of the vertices (i.e. the index lists for triangles) matters 26:04
- Use the left handed winding rule when constructing the triangle index list 27:08
- Introduction of the base class
Scene.hfor scene definitions its derived classes 28:50 - Remaining issues: concave shapes, triangle intersections, occlusion 31:10
- You can't easily sort this with sorting (although sorting has its place in 3d graphics)
- We will come back to these issues later in the series
Downloads
The GitHub repository for the tutorial code is here.
