GFX Part 4 - Introduction to Texturing in OpenGL ES

GFX Part 4 - Introduction to Texturing in OpenGL ES

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  TEXTURING
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  2014DEFINITION  Texture –A bitmap buffer in memory, usually containing color data  Textures are used for showing better realism in scenes GFX2014 Advanced Graphics Workshop, Bangalore
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  TEXTURES FOR REALISM 3
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  2014TEXTURING 3D OBJECTS Mapping from a bitmap to a 3D object involves matching the texture coordinates to the object surface  Texture coordinates are calculated along with the vertex coordinates  3D tools output Texture coordinates along with vertex information, for the scene Approach of data transfers
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  2014 CORRECT APPROACH OFDATA TRANSFERS 1. Generate Object (ex, glGenBuffers, glGenTextures) 2. Bind Object to an ID “xyz” (glBindBuffer(xyz), ..) 3. Transfer data to Object (glBufferData, glTexImage2D) 4. Unbind (glBindBuffer(0))   After this point, the data remains bound to “xyz” and is managed by GPU.  Can be accessed later by referencing “xyz”   Applies to VBOs, Textures, …  Note the implicit “no atomicity” – needs locking  Pixel Buffer Objects and performance subTexImage2D
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  2014HOW TO UPDATEREGIONS ?  It is possible to update selected regions of already uploaded textures  Using glTexSubImage2D  In embedded systems, not used widely  Performance implications of read-back path  Remember the client-server paradigm 6 Texture formats
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  2014TEXTURING BASICS  TextureFormats available  RGB* formats, Luminance only formats  Relevance of YUV  Texture Filtering  Maps texture coordinates to object coordinates – think of wrapping cloth over object  Mipmaps  Local optimisation – use pre-determined “reduced” size images, if object is far away from viewer – as compared to filtering full image  Objective is to reduce bandwidth, not necessarily higher quality  Application can generate and pass through TexImage2D() for multiple levels  GPU can generate using GenerateMipMap()  Occupies more memory Uv mapping
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  2014TEXTURING 2D OBJECTS Mapping from a bitmap to a rectangle is straightforward  0:1 range maps to 0:1 of object size  TexParameter determines filtering mode  TexParameter determines REPEAT  TexCoordinates determine if texture extends to full size of object or not S,T = {0:1} Upscaled Texcoords {0:10} + REPEAT texture object Non-image textures
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  2014NON-IMAGE TEXTURES  Texturesneed not be image data  Textures can be used to pass per-pixel “attributes” to the fragment shaders  Bump-maps and similar techniques for passing normal information  light-maps for lighting information  …. 9 compression
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  2014TEXTURE COMPRESSION TYPES GLES spec supports RGBA textures, Luminance …  To reduce memory bandwidth, compression used  Texture Compression major types  PVRTC, ETC1, Others  Android primarily supports ETC1  iOS supports PVRTC (and no other)  Extension support queryable using GL API queries  How to store this information in an uniform manner ?  Texture file formats  PVRTC (using Textool converter from IMG) commonly used  KTX file format KTX
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  2014KHRONOS KTX FILEFORMAT  To render a texture, steps to be used today:  Application needs apriori knowledge of texture type, format, storage type, mipmap levels, and filename or the buffer data itself  Then load into server using TexImage2D()  Proprietary formats exist to separate this application+texture dependency –  ex, PVRT from IMG  ETC from Ericsson  KTX file format from Khronos is a standard way to store texture information, and the texture itself  See next slide for structure of the file  http://www.khronos.org/opengles/sdk/tools/KTX/
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  2014KTX FORMAT … Passingcoords
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  2014TEXTURE COORDINATES TOGPU  Texture coordinates are passed to GPU as “Attributes” along with the vertices  Gen-bind-bufferdata, then bindAttrib  Quiz:  When does the binding actually come into effect ? WebGL/Textures
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  2014NOTE ON WEBGLAND TEXTURES  Because of the way file loads work on browsers (asynchronous), texture loading may not happen before the actual draw  Expect black screen for a very short-while till the Texture image loads from the website  On native applications, due to the synchronous nature of loading the texture this issue will not be present Programming
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  PROGRAMMING WITH TEXTURES bindTexture  pixelStorei (webGL only)  UNPACK_FLIP_Y_WEBGL  texImage2D  texParameteri  TEXTURE_MAG_FILTER  TEXTURE_MIN_FILTER  Note: WebGL “null” binding instead of “0”  Point Textures  Rectangular Texture
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  2014LAB L2 -TEXTURING