LECTURE 4. Announcements

Transcription

1 LECTURE 4 Announcements

2 Retries your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader your grader

3 To add textures Graphics Things graphics->addtexture( somename, :/images/sometexture.jpg ) Image needs to be placed in res/images and added to images.qrc file By default, textures are filtered. This doesn t look great for Minecraft graphics->gettexture( sometexture )-> setfiltermethod(texture::filter_method::nearest)

4 Minecraft 2 More rendering optimizations More collisions

5 LECTURE 4 Frustum Culling

6 Frustum Culling THE VIEW FRUSTUM

7 What is it? The volume of world objects that can actually be seen by the camera Shaped like a pyramid, bounded by: Far plane (the base of the frustum) Near plane (the cap of the frustum) Field of view/viewport size (determine the walls of the frustum)

8 What we re doing now During ondraw(): We tell OpenGL to render every single object Regardless of whether or not it will appear in the scene Can we avoid drawing some things?

9 What we should do Instead of telling OpenGL to draw everything, why don t we avoid sending that we know won t be drawn? What doesn t need to be drawn? Anything not in the view frustum! Only good if we can do this faster than it would take for OpenGL to draw everything

10 Extracting the View Frustum Frustum is defined by 6 planes Planes can be derived directly from the rows of our camera matrices You can get this using camera->getprojection() * camera->getview() Gives us a glm matrix Be careful glm uses column-major order, so use the coordinates given here to access the given cells / rows 0,0 1,0 2,0 3,0 0,1 1,1 2,1 3,1 0,2 1,2 2,2 3,2 0,3 1,3 2,3 3,3 Projection matrix view matrix r0 r1 r2 r3

11 Extracting the View Frustum Plane equation is given by a 4D vector (a,b,c,d): ax + by + cz + d = 0 The 6 clip planes of the frustum are defined below! 0,0 1,0 2,0 3,0 0,1 1,1 2,1 3,1 0,2 1,2 2,2 3,2 0,3 1,3 2,3 3,3 Projection matrix view matrix r0 r1 r2 r3 Clipping plane x y z +x +y +z Plane equation r3 r0 r3 r1 r3 r2 r3 + r0 r3 + r1 r3 + r2

12 Frustum Culling Test - General Compute 6 plane equations Should be updated whenever the camera changes! For each piece of scene geometry: Does the entire shape fall behind one of the planes? Skip rendering, it can t be seen!

13 Frustum Culling Test - AABB AABB (axis-aligned bounding box) Faces parallel to xy, xz, and yz planes Defined by a position and dimensions (convenient!) Rejection test: are all 8 corners behind any one plane? For point (x,y,z), behind plane if ax + by + cz + d < 0

14 Frustum Culling Test - Sphere Sphere Defined by a position and radius (which can just be one of your dimensions!) Rejection test: is the center (x,y,z) at least r units behind any one plane? If ax + by + cz + d < -r Planes must be normalized Divide (a,b,c,d) by a 2 + b 2 + c 2 You do not have to implement this! Minecraft is all about cubes! May be helpful later!

15 Implementation Notes Storing the r vectors In the camera? Only re-compute when camera changes Somewhere else? Up to you Design decisions yay!

16 Implementation Notes What should we cull? Individual blocks? Fine-grained Faster to just draw everything Whole chunks? Coarse-grained Far fewer culling tests Non-environment entities? Depends on # vertices If we have AABB s for them, depends on how many Required: per-chunk culling

17 Frustum Culling QUESTIONS?

18 LECTURE 4 Case Study Occlusion Culling

19 Occlusion Culling Frustum culling renders everything in the view frustum Occlusion culling renders only things that can be seen from camera, not just those inside the frustum (e.g. cuts out objects obscured by other objects) Unity Demo!

20 LECTURE 4 Collisions II

21 Collisions II COLLISIONS II

22 Last time on 3D Game Engines If two shapes are overlapping Make them not overlapping anymore Called non-continuous collision detection Objects teleport small distances in one tick there s no continuity from start to end, it all happens immediately

23 Shapes are moving towards each other Don t want them to ever overlap Only move them as much as they can go before colliding Called continuous collision detection Never allows shapes to be overlapping, no teleportation required The new model

24 Comparison to Non-Continuous Collision Continuous collision detection is often better for interacting with terrain (what we re doing this week) Won t miss any collisions This is good, because falling through the world is typically game breaking Typically depends on one of the objects being static Previous model is better for interactions of non-static objects May miss a few collisions Probably isn t a huge deal Doesn t know/care if either object is moving

25 Best of both worlds How can we mix and match? Make separate systems for terrain collision and objectobject collision CollisionSystem Collides objects with cylinder collision components VoxelSystem Collides moving player with static Chunks

26 Voxel Collision Detection Goal: collide the player with the terrain using continuous collision detection How do we implement this?

27 Voxel Collision Detection On a given tick Final position 1. Choose a direction (x, y, or z) 2. Iterate over all blocks the player would pass through, moving in this direction 3. If you encounter an impassable block, move the player to the boundary of that block If not, move them the full distance 4. Choose the next direction Starting position Blocks in the world Goal position

28 Example: X-axis Collision Sweep Top Solid block Bottom Player Player Move Check player Check as these back far these as first by it second epsilon can ( ) go Y X

29 Example: X-axis Collision Sweep Things to note 1. Amount that the player wants to move in x direction in one tick is velocity.x * seconds velocity.y * seconds for y direction velocity.z * seconds for z direction 2. The player passes through multiple cells in the y dimension, as it makes one step in the x direction In three dimensions, the player will pass through multiple cells in the y and z dimensions as it makes one step in the x direction Need to check all of these cells for impassable blocks 3. Player is moving in increasing x, so check cells in that order

30 Implementation Tips Need to sweep in x, y, and z, directions but implement the y-sweep first Easier to debug horizontal movement if you can stand on a floor If a collision is found, move the player away from the point of collision by small amount Along surface normal multiplied by small epsilon

31 Implementation Tips Be careful at chunk boundaries Player may be colliding with blocks in multiple chunks Use your 3 rd person camera to debug Visualize the player s shape to *see* collisions Don t be afraid to restart The actual code isn t too long (can be as little as ~20 lines for each axis sweep test) Lots of places you can be off by 1 block or by epsilon

32 Pseudocode: Collision Sweep // Sweep test in y direction void VoxelSystem::ySweep(float seconds, GameObject *obj) { // TODO: initialize start and end x, z, positions (based on dimensions and position) int startx, startx, endz, endz; // TODO: initialize start and end y position (based on dimensions, position, velocity and seconds) int starty, endy; // TODO: initialize direction of y motion, +1 or -1 int step; // Loop and check for collisions for(y = starty; y!= (endy + step); y += step) { for(x = startx; x <= endx; x++) { for(z = startz; z <= endz; z++) { if(!voxelsystem::ispassable(x, y, z)) { // TODO: translate to collision point (minus small epsilon) break; } } } } } // TODO: If no collision, move object full distance

33 Collisions II QUESTIONS?

34 LECTURE 4 Tips for Minecraft 2

35 Frustum Culling Can be incorporated into default DrawSystem, or a DrawSystem just for Chunks

36 Collisions May be helpful to have ispassable(x, y, z) method in your VoxelSystem For the Chunk that has the block at (x, y, z) in the world, see if it is passable Can use this in your collision sweep methods instead of checking specific Chunks

37 LECTURE 4 C++ Tip of the Week

38 Static Very helpful C/C++ keyword Behavior of static can vary a lot depending on use Member variable vs namespace variable vs local variable causes different results

39 More Static Static variables exist for the "lifetime" of the translation unit that it's defined in Translation unit: simplest unit of compilation Consists of the contents of a single source file, plus the contents of any header files directly or indirectly included Result: static variables have a single instance (usually)

40 Namespace Static If variable is outside of any functions or class, it can't be accessed from any other translation unit This is known as "internal linkage" NEVER do this in headers you end up with a separate variable in each translation unit (i.e., every time you include the header) static int x; class Foo { public: void bar(); };

41 Member Variables and static A static member variable is shared between all instances of the class Important: you need to both declare and define static member variables

42 Bad //in.h file class Foo { public: static int x; void bar(); }; //in.cpp file void Foo::bar(){ Foo::x = 10; }; Good //in.h file class Foo { public: static int x; void bar(); }; //in.cpp file int Foo::x = 0; void Foo::bar(){ Foo::x = 10; };

43 Static functions Less confusing Same as in Java A static function can be called without an instance of a class Cannot access non-static member variables class Foo { private: static int value; public: static int getvalue() { return value; } };

44 Const Another very helpful keyword Declares a constant int x = 4; //normal int const int y = x; //value of y cannot be changed const int* foo = &y; //can t change value of y int *const bar = &x; //can t reassign bar const int *const yum = foo; //can t change anything

45 Const member functions Const++ void Entity::draw() const { // can t change Entity Very, very good style Using const references in functions void Entity::accelerate(const vec3 &acc) { Only const functions can be called on const references Much cheaper than accelerate(vec3 acc)

46 MINECRAFT1 PLAYTESTING To the Sunlab!