Week 2 - Monday CS361

Last time What did we talk about last time? C# MonoGame

Questions?

More MonoGame Examples

Review of MonoGame Program creates a Game1 (or similar) object and starts it running Game1 has: Initialize() LoadContent() Update() Draw() It runs an update-draw loop continuously until told to exit

Drawing text Modern TrueType and OpenType fonts are vector descriptions of the shapes of characters Vector descriptions are good for quality, but bad for speed MonoGame allows us to take a vector-based font and turn it into a picture of characters that can be rendered as a texture Just like everything else

Drawing text continued Inside a MonoGame project, right-click the Content.mgcb file and choose Open with… Select MonoGame Pipeline Tool Right click on Content in the tool, and select Add -> New Item… Choose SpriteFont Description and give your new SpriteFont a name Open the spritefont file, choosing a text editor like Notepad++ By default, the font is Arial at size 12 Edit the XML to pick the font, size, and spacing You will need multiple Sprite Fonts even for different sizes of the same font Repeat the process to make more fonts Note: fonts have complex licensing and distribution requirements

Drawing a font continued Load the font similar to texture content Add a DrawString() call in the Draw() method: font = Content.Load<SpriteFont>("Text"); spriteBatch.Begin(); spriteBatch.DrawString(font, "Hello, World!", new Vector2(100, 100), Color.Black); spriteBatch.End();

Why are they called sprites? They "float" above the background like fairies… Multiple sprites are often stored on one texture It's cheaper to store one big image than a lot of small ones This is an idea borrowed from old video games that rendered characters as sprites

Drawing sprites with rotation It is possible to apply all kinds of 3D transformations to a sprite A sprite can be used for billboarding or other image-based techniques in a fully 3D environment But, we can also simply rotate them using an overloaded call to Draw() spriteBatch.Draw(texture, location, sourceRectangle, Color.White, angle, origin, 1.0f, SpriteEffects.None, 1);

Let's unpack that texture: Texture2D to draw location: Location to draw it sourceRectangle Portion of image Color.White Full brightness angle Angle in radians origin Origin of rotation 1.0f Scaling SpriteEffects.None No effects 1 Float level

Student Lecture: Graphics Rendering Pipeline and Application Stage

Graphics Rendering Pipeline

Rendering What do we have? What do we want? Virtual camera (viewpoint) 3D objects Light sources Shading Textures What do we want? 2D image

Pipelines The idea of a pipeline is to divide a task into independent steps, each of which can be performed by dedicated hardware Example RISC pipeline: Instruction fetch Decode Execute Memory Access Writeback

Pipeline performance If you have an n stage pipeline, what's the maximum speedup you can get? Consider a TV show with the following pipeline Write Rewrite Film Edit Assume each step takes 1 week How much total time does it take to produce a 13 episode season? What if there was no pipelining? Note that a pipeline's speed is limited by its slowest stage, the bottleneck

Graphics rendering pipeline For API design, practical top-down problem solving, and hardware design, and efficiency, rendering is described as a pipeline This pipeline contains three conceptual stages: Produces material to be rendered Application Decides what, how, and where to render Geometry Renders the final image Rasterizer

Architecture These conceptual stages may or may not be running at the same time Each conceptual stage may contain its own internal pipelines or parallel execution

Speed A critical concern of real time rendering is the rendering speed, determined by the slowest stage in the pipeline We can measure speed in frames per second (fps), common for average performance over time We can also measure speed in Hertz (Hz), common for hardware

Rendering speed example Output device has a maximum update frequency of 60 Hz (very common for LCD's) The bottleneck rendering stage is 62.5 ms What's our rendering speed? 1/0.0625 = 16 fps 60/1 = 60 fps 60/2 = 30 fps 60/3 = 20 fps 60/4 = 15 fps 60/5 = 12 fps

Application Stage

Application stage The application stage is the stage completely controlled by the programmer As the application develops, many changes of implementation may be done to improve performance The output of the application stage are rendering primitives Points Lines Triangles

Important jobs of the application stage Reading input Managing non-graphical output Texture animation Animation via transforms Collision detection Updating the state of the world in general

Acceleration The Application Stage also handles a lot of acceleration Most of this acceleration is telling the renderer what NOT to render Acceleration algorithms Hierarchical view frustum culling BSP trees Quadtrees Octrees

Hierarchical view frustum culling An application can remove those objects that are not in the cone of visibility Hierarchies of objects can be used to make these calculations easier

BSP Trees Splitting planes are made through polygons to repeatedly subdivide the polygons in a scene in half Often, BSP Trees are calculated a single time for complex, static scenes

Quadtrees and Octrees Like BSP's, the space can be repeatedly subdivided as long as it contains a number of objects above a certain threshold Octrees divide the space in three dimensions while quadtrees only focus on two

Upcoming

Next time… Rendering pipeline Geometry stage

Reminders Pick your teams today if you haven't already! Keep reading Chapter 2 Focus on 2.3