the gamedesigninitiative at cornell university Lecture 12 Scene Graphs

Transcription

1 Lecture 12

2 Aside: When Do We Load Assets? Main Application Application Start-up Level Load GameMode GameMode Models Scene Choice affects design Models Scene & ownership of asset manager 2

3 Drawing in CUGL Use draw() method Called after update() Clears screen first Uses clear color field Can use any OpenGL Included in CUBase.h Best to use OpenGLES (subset of OpenGL) Or use a SpriteBatch Mostly like in 3152 void draw() { glenablevertexattribarray(0); glbindbuffer(gl_array_buffer, vertexbuffer); glvertexattribpointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0 ); gldrawarrays(gl_triangles, 0, 3); gldisablevertexattribarray(0); } void draw() { batch->begin(); batch->draw(image1,vec2(10,10)); batch->draw(image2,vec2(50,20)); batch->end(); } 3

4 The Scene Graph Or any subclass Scene 4

5 Each is a Coordinate System Bounded box inside Scene Game Camera 5 Coords relative to parent box

6 Each is a Coordinate System Scene 6

7 Each is a Coordinate System Scene Scene 7

8 Each is a Coordinate System Scene Origin Origin Origin Origin 8

9 Settings Pass Down Graph Scene Transforms on parent also transform children 9

10 Settings Pass Down Graph Scene Transparency on parent also applies to children 10

11 Settings Pass Down Graph Scene Disabling parent also disables children 11

12 Rendering a Scene is Easy scene->render(batch) Uses SpriteBatch to draw Calls begin()/end() for you Sets SpriteBatch camera Limits in-between drawing Uses a preorder traversal Draws a parent node first Draws children in order Parent acts as background 1 Scene

13 How Does a SpriteBatch Work? Sprites = textured triangles Gar all sprite vertices Make one list of triangles Send m to GPU at once But stall on texture change Reorder data on texture Draw texture all at once Limits texture switches Safe if re is no overlap Hence name! 13

14 How Does a SpriteBatch Work? Sprites = textured triangles Gar all sprite vertices Make one list of triangles Send m to GPU at once But stall on texture change Reorder data on texture Draw texture all at once Limits texture switches Safe if re is no overlap Hence name! 14

15 How Does a SpriteBatch Work? Sprites = textured triangles Gar all sprite vertices Make one list of triangles Send m to GPU at once But stall on texture change Reorder data on texture Draw texture all at once Limits texture switches Safe if re is no overlap Hence name! 15

16 How Does a SpriteBatch Work? Sprites = textured triangles Gar all sprite vertices Make one list of triangles Send m to GPU at once But stall on texture change Reorder data on texture Draw texture all at once Limits texture switches Safe if re is no overlap Hence name! 16

17 How Does a SpriteBatch Work? Sprites = textured triangles Gar all sprite vertices Make one list of triangles Send m to GPU at once But stall on texture change Reorder data on texture Draw texture all at once Limits texture switches Safe if re is no overlap Hence name! 17

18 Optimizing Performance: zorder SpriteBatch defers to Scene Scene determines order Reordering a scene is bad Give hints to Scene Give each child a z-value Ties are permitted sortzorder() sorts tree Can make this automatic Controls texture switching One texture = one z-value Reduces it to one draw call 18

19 Optimizing Performance: Atlases Idea: Never switch textures Film strip is many images We can draw part of texture One texture for everything? Called a texture atlas Disadvantages? Cannot tile textures Can be tricky to pack Ideal for interface design Images for UX widgets Often small and compact 19

20 Making Custom Graph s CUGL has many node types Animation (animation) Wire (wireframes) Polygon (tiled shapes) Path (lines with width) All one graph node Label (text) Use ir code as a guide Two main methods needed draw() generaterenderdata() 20

21 generaterenderdata() Drawing data is cached No state change in draw() When do we update The vertex positions The vertex colors The texture coordinates In generaterenderdata() Used in setters as helper Ensures cache consistency Is node specific /** * Illustrate drawing in OpenGL */ void doopengl() { // Tell OpenGL where data is glenablevertexattribarray(0); glbindbuffer(.); glvertexattribpointer( ); } // Tell OpenGL to draw data gldrawarrays( ); // Tell OpenGL to forget data gldisablevertexattribarray(0); 21

22 The draw() Method void Custom::draw(const std::shared_ptr<spritebatch>& batch, const Mat4& transform, Color4 tint) { if (!_rendered) { generaterenderdata(); } batch->setcolor(tint); batch->settexture(_texture); batch->setblendequation(_blendequation); batch->setblendfunc(_srcfactor, _dstfactor); } 22 batch->fill(_vertices, _vertsize, 0, _indices, _indxsize, 0, transform);

23 The draw() Method void Custom::draw(const std::shared_ptr<spritebatch>& batch, const Mat4& transform, Color4 tint) { if (!_rendered) { generaterenderdata(); } Computed from parent (+camera) batch->setcolor(tint); batch->settexture(_texture); batch->setblendequation(_blendequation); batch->setblendfunc(_srcfactor, _dstfactor); Computed from parent (+scene) } 23 batch->fill(_vertices, _vertsize, 0, _indices, _indxsize, 0, transform); The Render Data

24 Why Use a Scene Graph? Animation is much easier! Can reduce filmstrips Break asset into parts Each has a coord system Transform each separately Decouple animation loop Update does not set frame advances frame Update switches animations Example: RagDoll 24

25 Why Use a Scene Graph? Animation is much easier! Can reduce filmstrips Break asset into parts Each has a coord system Transform each separately Decouple animation loop Update does not set frame advances frame Update switches animations Example: RagDoll 25

26 Why Use a Scene Graph? Animation is much easier! Can reduce filmstrips Break asset into parts Each has a coord system Transform each separately Decouple animation loop Update does not set frame advances frame Update switches animations Example: RagDoll 26

27 Why Use a Scene Graph? Animation is much easier! Can reduce filmstrips Break asset into parts Each has a coord system Transform each separately Decouple animation loop Update does not set frame advances frame Update switches animations Example: RagDoll 27

28 Also Good for Touch Interfaces Touch handler requires Which object touched Location inside object Scene graph is a search tree Check if touch is in parent n check each child Faster than linear search But limit this to a search No input control in node Polling over callbacks Scene 28

29 in Games Historically designed for animators Can easily manipulate without using code Cocos2D made it an architectural centerpiece Made loading complex animation easy Made engine amenable to graphical editors Unity3D adopted idea for 3D games Idea is roughly same as 2D version But z-order optimizations are no longer valid 29

30 The Cocos2D Philosophy Scene Each model is its own node coords = texture coords Model pos = node pos Physics Sprite Physics Sprite Physics Sprite Physics Sprite Physics Sprite Each node is a Box2D body Scene is a Box2D world s moved automatically Each node processes input has custom listener Gets touches on that node Massive violation of MVC 30

31 The Cocos2D Philosophy Scene Each model is its own node coords = texture coords Model pos = node pos Physics Sprite Physics Sprite Physics Sprite Physics Sprite Physics Sprite Each node is a Box2D body Scene is a Box2D world s moved automatically Each node processes input has custom listener Gets touches on that node Massive violation of MVC 31

32 The Problem: Physics 2D Physics Island Parallax layers (e.g. beat-em up) 32

33 The Problem: Physics 2D Physics Island Separate Island Parallax layers (e.g. beat-em up) 33

34 The Problem: Physics 34

35 The Problem: Physics How big is that scene graph? 35

36 Summary CUGL tries to leverage ideas from 3152 Top level class works like classic GDXRoot Design architecture to switch between modes Use SpriteBatch class to draw textures in 2D. New idea is using scene graphs to draw Tree of nodes with relative coordinate systems Makes decompositional animation easier Makes touch input easier to process CUGL decouples scene graphs from physics 36