glm (1124588), страница 4
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Matrix types store their values in column-major order.This is useful for uploading data to matrices or copying data to buffer objects.Example:#include <glm/glm.hpp>#include <glm/gtc/type_ptr.hpp>glm::vec3 aVector(3);glm::mat4 someMatrix(1.0);glUniform3fv(uniformLoc, 1, glm::value_ptr(aVector));glUniformMatrix4fv(uniformMatrixLoc,1, GL_FALSE, glm::value_ptr(someMatrix));<glm/gtc/type_ptr.hpp>need to be included to use these features.4.15. GLM_GTC_ulpAllow the measurement of the accuracy of a function against a referenceimplementation. This extension works on floating-point data and provides results inULP.<glm/gtc/ulp.hpp>need to be included to use these features.5. Known issues5.1. not functionThe GLSL keyword not is also a keyword in C++.
To prevent name collisions, ensurecross compiler support and a high API consistency, the GLSL not function has beenimplemented with the name not_.5.2. half based types and component accessesGLM supports half float number types through the extension GLM_GTC_half_float.This extension provides the types half, hvec*, hmat*x* and hquat*.Unfortunately, C++98 specification doesn’t support anonymous unions which limitshvec* vector components access to x, y, z and w.However, Visual C++ does support anonymous unions if the language extensions areenabled (/Za to disable them).
In this case GLM will automatically enables thesupport of all component names (x,y,z,w ; r,g,b,a ; s,t,p,q).To uniformalize the component access across types, GLM provides the defineGLM_FORCE_ONLY_XYZW which will generates errors if component accesses aredone using r,g,b,a or s,t,p,q.#define GLM_FORCE_ONLY_XYZW#include <glm/glm.hpp>6. FAQ6.1 Why GLM follows GLSL specification and conventions?Following GLSL conventions is a really strict policy of GLM.
It has been designedfollowing the idea that everyone does its own math library with his own conventions.The idea is that brilliant developers (the OpenGL ARB) worked together and agreedto make GLSL. Following GLSL conventions is a way to find consensus. Moreover,basically when a developer knows GLSL, he knows GLM.6.2. Does GLM run GLSL program?No, GLM is a C++ implementation of a subset of GLSL.6.3. Does a GLSL compiler build GLM codes?No, this is not what GLM attends to do!6.4. Should I use ‘GTX’ extensions?GTX extensions are qualified to be experimental extensions.
In GLM this means thatthese extensions might change from version to version without any restriction. Inpractice, it doesn’t really change except time to time. GTC extensions are stabled,tested and perfectly reliable in time. Many GTX extensions extend GTC extensionsand provide a way to explore features and implementations and APIs and then arepromoted to GTC extensions. This is fairly the way OpenGL features are developed;through extensions.6.5.
Where can I ask my questions?A good place is the OpenGL Toolkits forum on OpenGL.org6.6. Where can I find the documentation of extensions?The Doxygen generated documentation includes a complete list of all extensionsavailable. Explore this API documentation to get a complete view of all GLMcapabilities!6.7. Should I use ‘using namespace glm;’?NO! Chances are that if ‘using namespace glm;’ is called, especially in a header file,name collisions will happen as GLM is based on GLSL which uses common tokens fortypes and functions.
Avoiding ‘using namespace glm;’ will a higher compatibility withthird party library and SDKs.6.8. Is GLM fast?First, GLM is mainly designed to be convenient and that's why it is written againstGLSL specification. Following the 20-80 rules where 20% of the code grad 80% of theperformances, GLM perfectly operates on the 80% of the code that consumes 20% ofthe performances. This said, on performance critical code section, the developerswill probably have to write to specific code based on a specific design to reach peakperformances but GLM can provides some descent performances alternatives basedon approximations or SIMD instructions.6.9. When I build with Visual C++ with /W4 warning level, I havewarnings...You should not have any warnings even in /W4 mode.
However, if you expect suchlevel for you code, then you should ask for the same level to the compiler by at leastdisabling the Visual C++ language extensions (/Za) which generates warnings whenused. If these extensions are enabled, then GLM will take advantage of them and thecompiler will generate warnings.7. Code samplesThis series of samples only shows various GLM features without consideration of anysort.7.1.
Compute a triangle normal#include <glm/glm.hpp> // vec3 normalize crossglm::vec3 computeNormal(glm::vec3 const & a,glm::vec3 const & b,glm::vec3 const & c){return glm::normalize(glm::cross(c - a, b - a));}// A much faster but less accurate alternative:#include <glm/glm.hpp> // vec3 cross#include <glm/gtx/fast_square_root.hpp> // fastNormalizeglm::vec3 computeNormal(glm::vec3 const & a,glm::vec3 const & b,glm::vec3 const & c){return glm::fastNormalize(glm::cross(c - a, b - a));}7.2. Matrix transform// vec3, vec4, ivec4, mat4#include <glm/glm.hpp>// translate, rotate, scale, perspective#include <glm/gtc/matrix_transform.hpp>// value_ptr#include <glm/gtc/type_ptr.hpp>void setUniformMVP(GLuint Location,glm::vec3 const & Translate,glm::vec3 const & Rotate){glm::mat4 Projection =glm::perspective(45.0f, 4.0f / 3.0f, 0.1f, 100.f);glm::mat4 ViewTranslate = glm::translate(glm::mat4(1.0f),Translate);glm::mat4 ViewRotateX = glm::rotate(ViewTranslate,Rotate.y, glm::vec3(-1.0f, 0.0f, 0.0f));glm::mat4 View = glm::rotate(ViewRotateX,Rotate.x, glm::vec3(0.0f, 1.0f, 0.0f));glm::mat4 Model = glm::scale(glm::mat4(1.0f),glm::vec3(0.5f));glm::mat4 MVP = Projection * View * Model;glUniformMatrix4fv(Location, 1, GL_FALSE, glm::value_ptr(MVP));}7.3.
Vector types#include <glm/glm.hpp> //vec2#include <glm/gtc/type_precision.hpp> //hvec2, i8vec2, i32vec2std::size_t const VertexCount = 4;// Float quad geometrystd::size_t const PositionSizeF32 = VertexCount * sizeof(glm::vec2);glm::vec2 const PositionDataF32[VertexCount] ={glm::vec2(-1.0f,-1.0f),glm::vec2( 1.0f,-1.0f),glm::vec2( 1.0f, 1.0f),glm::vec2(-1.0f, 1.0f)};// Half-float quad geometrystd::size_t const PositionSizeF16 = VertexCount * sizeof(glm::hvec2);glm::hvec2 const PositionDataF16[VertexCount] ={glm::hvec2(-1.0f, -1.0f),glm::hvec2( 1.0f, -1.0f),glm::hvec2( 1.0f, 1.0f),glm::hvec2(-1.0f, 1.0f)};// 8 bits signed integer quad geometrystd::size_t const PositionSizeI8 = VertexCount * sizeof(glm::i8vec2);glm::i8vec2 const PositionDataI8[VertexCount] ={glm::i8vec2(-1,-1),glm::i8vec2( 1,-1),glm::i8vec2( 1, 1),glm::i8vec2(-1, 1)};// 32 bits signed integer quad geometrystd::size_t const PositionSizeI32 = VertexCount * sizeof(glm::i32vec2);glm::i32vec2 const PositionDataI32[VertexCount] ={glm::i32vec2(-1,-1),glm::i32vec2( 1,-1),glm::i32vec2( 1, 1),glm::i32vec2(-1, 1)};7.4.
Lighting#include <glm/glm.hpp> // vec3 normalize reflect dot pow#include <glm/gtx/random.hpp> // vecRand3// vecRand3, generate a random and equiprobable normalized vec3glm::vec3 lighting(intersection const & Intersection,material const & Material,light const & Light,glm::vec3 const & View){glm::vec3 Color = glm::vec3(0.0f);glm::vec3 LightVertor = glm::normalize(Light.position() - Intersection.globalPosition() +glm::vecRand3(0.0f, Light.inaccuracy());if(!shadow(Intersection.globalPosition(),Light.position(),LightVertor)){float Diffuse = glm::dot(Intersection.normal(), LightVector);if(Diffuse <= 0.0f)return Color;if(Material.isDiffuse())Color += Light.color() * Material.diffuse() * Diffuse;if(Material.isSpecular()){glm::vec3 Reflect = glm::reflect(-LightVector,Intersection.normal());float Dot = glm::dot(Reflect, View);float Base = Dot > 0.0f ? Dot : 0.0f;float Specular = glm::pow(Base, Material.exponent());Color += Material.specular() * Specular;}}return Color;}8.
References8.1. GLM development- GLM website- GLM HEAD snapshot- GLM bug report and feature request- G-Truc Creation’s page8.2. OpenGL specifications- OpenGL 4.3 core specification- GLSL 4.30 specification- GLU 1.3 specification8.3. External links- The OpenGL Toolkits forum to ask questions about GLM8.4. Projects using GLM- Outerra:3D planetary engine for seamless planet rendering from space down to the surface.Can use arbitrary resolution of elevation data, refining it to centimeter resolutionusing fractal algorithms.- opencloth:A collection of source codes implementing cloth simulation algorithms in OpenGL.- OpenGL 4.0 Shading Language Cookbook:A full set of recipes demonstrating simpleand advanced techniques for producinghigh-quality, real-time 3D graphics usingGLSL 4.0.How to use the OpenGL Shading Languageto implement lighting and shadingtechniques.Use the new features of GLSL 4.0including tessellation and geometryshaders.How to use textures in GLSL as part of awide variety of techniques from basictexture mapping to deferred shading.Simple, easy-to-follow examples withGLSL source code, as well as a basicdescription of the theory behind eachtechnique.- Are you using GLM in a project?8.5.
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