Week 1 -Wednesday What did we talk about last time? Introduction to - PowerPoint PPT Presentation

Week 1 -Wednesday

 What did we talk about last time?  Introduction to the course  Colors  RGB  CMYK  HSL and HSV

 We will be thinking of images as linear buffers of data (which will usually store R,G,B and sometimes A values for each pixel)  Bitmaps ( .bmp files) are almost that simple  Most common image formats ( .jpg , .png , and .gif files) are more complex  They use different forms of compression to keep the image size small  Otherwise, an 800 x 600 image is 3 bytes per pixel x 800 x 600 = 1,440,000 bytes > 1 MB

 Stands for J oint P hotographic E xperts G roup  Good for images without too much high contrast (sharp edges)  Photographs are often stored as JPEGs  Uses crazy math (discrete cosine transform) to reduce the amount of data needed  Lossy compression

 Good for images with low numbers of colors and high contrast differences  Has built-in compression sort of like zip files  Similar to the older GIF ( .gif ) images  GIFs are unpopular now because they only support 256 colors  GIFs also suffered from legal battles over the algorithm used for compression  Lossless compression

 Tagged image file format ( .tiff or .tif ) images are another standard sometimes used in computer graphics or for scanned images  The TIFF standard is really crazy, supporting layers, LZW style compressions, JPEG style compression  DirectDraw surface container ( .dds ) files were designed for DirectX, allowing for the S3 Texture Compression algorithm  The pixel data is easily to decompress in hardware  TARGA ( .tga ) files have a very simple structure and are still used for some textures

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

 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 1. 2. Decode Execute 3. 4. Memory Access 5. Writeback

 If you have an n stage pipeline, what's the maximum speedup you can get?  Consider a TV show with the following pipeline Write 1. Rewrite 2. Film 3. Edit 4.  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

 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: Decides Produces what, Renders material how, and the final Application Geometry Rasterizer to be where to image rendered render

 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

 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

 Output device has a maximum update frequency of 60 Hz (very common for LCDs)  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

 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

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

 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

 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

 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

 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

 C# and MonoGame overview

 No required reading ahead of time  But, checking out MonoGame is not a bad idea  To run it on your own machine, you'll need Visual Studio 2015 Community  Freely available  Alternatively, you can talk to Professor Stucki about getting the Enterprise edition, but those features won't be useful for this class