CS计算机代考程序代写 compiler c++ c/c++ GPU This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License
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Computer Graphics
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The GLSL API
Mike Bailey mjb@cs.oregonstate.edu
glslapi.pptx
mjb – December 15, 2020
The GLSL Shader-Creation Process
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Computer Graphics
mjb – December 15, 2020
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Initializing the GL Extension Wrangler (GLEW)
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#include “glew.h“ …
GLenum err = glewInit(); if( err != GLEW_OK )
{
fprintf( stderr, “glewInit Error\n” ); exit( 1 );
}
fprintf( stderr, “GLEW initialized OK\n” );
fprintf( stderr, “Status: Using GLEW %s\n”, glewGetString(GLEW_VERSION) );
Do this immediately after opening the window
GLEW cannot be initialized until a graphics window is open. Like OpenGL itself, GLEW’s calls will not work unless it can see a graphics context (i.e., a graphics state).
Computer Graphics
http://glew.sourceforge.net
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Reading a Shader source file into a character array
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#include
FILE *fp = fopen( filename, “r” ); if(fp==NULL) {…}
fseek( fp, 0, SEEK_END );
int numBytes = ftell( fp ); // length of file
GLchar * buffer = new GLchar [numBytes+1];
rewind( fp ); // same as: “fseek( in, 0, SEEK_SET )”
fread( buffer, 1, numBytes, fp );
fclose( fp );
buffer[numBytes] = ‘\0‘; // the entire file is now in a byte string
Computer Graphics
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Creating and Compiling a Vertex Shader from that character buffer 5 (Geometry and Fragment files work the same way)
This is the only part of this process that is specific to the type of shader it is
int status;
int logLength;
GLuint vertShader = glCreateShader( GL_VERTEX_SHADER );
glShaderSource( vertShader, 1, (const GLchar **)&buffer, NULL );
delete [ ] buffer;
glCompileShader( vertShader ); CheckGlErrors( “Vertex Shader 1” );
An array of strings
glGetShaderiv( vertShader, GL_COMPILE_STATUS, &status ); if( status == GL_FALSE )
{
fprintf( stderr, “Vertex shader compilation failed.\n” );
glGetShaderiv( vertShader, GL_INFO_LOG_LENGTH, &logLength ); GLchar *log = new GLchar [logLength];
glGetShaderInfoLog( vertShader, logLength, NULL, log );
fprintf( stderr, “\n%s\n”, log );
delete [ ] log;
exit( 1 );
}
CheckGlErrors( “Vertex Shader 2” );
Computer Graphics
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Creating Different Shader Types
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GLuint shader = glCreateShader( GL_VERTEX_SHADER );
GLuint shader = glCreateShader( GL_GEOMETRY_SHADER );
GLuint shader = glCreateShader( GL_TESS_CONTROL_SHADER ); GLuint shader = glCreateShader( GL_TESS_EVALUATION_SHADER ); GLuint shader = glCreateShader( GL_FRAGMENT_SHADER );
GLuint shader = glCreateShader( GL_COMPUTE_SHADER );
Other than this, the rest of the create, compile, link process is the same for each shader type.
Computer Graphics
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How does that array-of-strings thing work?
These are two ways to provide a single buffer:
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GLchar *ArrayOfStrings[3];
ArrayOfStrings[0] = “#define SMOOTH_SHADING”; ArrayofStrings[1] = “ . . . a commonly-used procedure . . . “; ArrayofStrings[2] = “ . . . the real vertex shader code . .. “; glShaderSource( vertShader, 3, ArrayofStrings, NULL );
GLchar *buffer[1];
buffer[0] = “ . . . the entire shader code . . . “; glShaderSource( vertShader, 1, buffer, NULL );
GLchar *buffer = “ . . . the entire shader code . . . “; glShaderSource( vertShader, 1, (const GLchar **)&buffer, NULL );
Computer Graphics
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1.
2. 3.
Why use an array of strings as the shader input, instead of just a single string?
You can use the same shader source and insert the appropriate “#defines” at the beginning
You can insert a common header file (≈ a .h file)
You can simulate a “#include” to re-use common pieces of code
if-tests vs. preprocessing
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if( Mode == SmoothShading ) {…}
else if( Mode == PhongShading ) {…}
Computer Graphics
#ifdef SMOOTH_SHADING {…}
#endif
#ifdef PHONG_SHADING {…}
#endif
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Creating the Program and Attaching the Shaders to It
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GLuint program = glCreateProgram( ); glAttachShader( program, vertShader ); glAttachShader( program, fragShader ); glAttachShader( program, geomShader );
Computer Graphics
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Linking the Program and Checking its Validity
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glLinkProgram( program );
CheckGlErrors( “Shader Program 1” );
glGetProgramiv( program, GL_LINK_STATUS, &status ); if( status == GL_FALSE )
{
fprintf( stderr, “Link failed.\n” );
glGetProgramiv( program, GL_INFO_LOG_LENGTH, &logLength ); log = new GLchar [logLength];
glGetProgramInfoLog( program, logLength, NULL, log );
fprintf( stderr, “\n%s\n”, log );
delete [ ] log;
exit( 1 );
}
CheckGlErrors( “Shader Program 2” );
glValidateProgram( program );
glGetProgramiv( program, GL_VALIDATE_STATUS, &status );
fprintf( stderr, “Program is %s.\n”, status == GL_FALSE ? “invalid” : “valid” );
Computer Graphics
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Making the Program Active
glUseProgram( program );
Making the Program Inactive
(use the fixed function pipeline instead)
glUseProgram( 0 );
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Using Multiple Shader Programs
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glUseProgram( program0 );
glUseProgram( program1 );
glUseProgram( program2 );
glUseProgram( program3 );
glUseProgram( program4 );
glUseProgram( program5 );
A specified shader program is an “attribute” – it stays in effect until you change it
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Passing in Uniform Variables
You first need to find the variable’s location in the shader program’s symbol table.
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float lightLoc[3] = { 0., 100., 0. };
GLint location = glGetUniformLocation( program, “uLightLocation” );
if( location < 0 ) fprintf( stderr, “Cannot find Uniform variable ‘uLightLocation’\n” ); else glUniform3fv( location, 1, lightLoc ); Then you need to fill it. Computer Graphics mjb – December 15, 2020 13 Passing in Attribute Variables You first need to find the variable’s location in the shader program’s symbol table. 14 GLint location = glGetAttribLocation( program, “aArray” ); if( location < 0 ) { fprintf( stderr, “Cannot find Attribute variable ‘aArray’\n” ); } else { glEnd(); } glBegin( GL_TRIANGLES ); glVertexAttrib2f( location, a0, b0 ); glVertex3f( x0, y0, z0 ); glVertexAttrib2f( location, a1, b1 ); glVertex3f( x1, y1, z1 ); glVertexAttrib2f( location, a2, b2 ); glVertex3f( x2, y2, z2 ); Then you need to fill it per-vertex. Computer Graphics mjb – December 15, 2020 14 7 Checking for Errors 15 void CheckGlErrors( const char* caller ) { unsigned int glerr = glGetError(); if( glerr == GL_NO_ERROR ) return; fprintf( stderr, "GL Error discovered from caller ‘%s‘: ", caller ); switch( glerr ) { } } case GL_INVALID_ENUM: fprintf( stderr, "Invalid enum.\n" ); break; case GL_INVALID_VALUE: fprintf( stderr, "Invalid value.\n" ); break; case GL_INVALID_OPERATION: fprintf( stderr, "Invalid Operation.\n" ); break; case GL_STACK_OVERFLOW: fprintf( stderr, "Stack overflow.\n" ); break; case GL_STACK_UNDERFLOW: fprintf(stderr, "Stack underflow.\n" ); break; case GL_OUT_OF_MEMORY: fprintf( stderr, "Out of memory.\n" ); break; default: fprintf( stderr, “Unknown OpenGL error: %d (0x%0x)\n”, glerr, glerr ); Computer Graphics It’s not a bad idea to do this in all your OpenGL programs, even without shaders! mjb – December 15, 2020 15 Writing a C++ Class to Handle Everything is Fairly Straightforward 16 Setup: int Polar; float K; GLSLProgram *Hyper = new GLSLProgram( ); bool valid = Hyper->Create( “hyper.vert”, “hyper.geom”, “hyper.frag” ); if( ! valid ) { . . . }
This loads, compiles, and links the shader. It prints error messages if something went wrong.
Using the GPU program:
Reverting to the fixed-function pipeline during display: ComHpuytepreGrr-a>pUhicsse( 0 );
Hyper->Use( );
Hyper->SetUniformVariable( “uPolar”, Polar ); Hyper->SetUniformVariable( “uK”, K ); glBegin( GL_TRIANGLES );
Hyper->SetAttributeVariable( “aTemperature”, T0 ); glVertex3f( x0, y0, z0 ); Hyper->SetAttributeVariable( “aTemperature”, T1 ); glVertex3f( x1, y1, z1 ); Hyper->SetAttributeVariable( “aTemperature”, T2 ); glVertex3f( x2, y2, z2 );
glEnd( );
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GLSL Source
Computer Graphics
SPIR-V
Vendor-specific code
mjb – December 15, 2020
External GLSL Compiler
SPIR-V
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SPIR-V is a file format that can be used to hold shader code that has been pre-compiled, but has not yet been turned into machine code. It was created as a way for software developers to pre-compile their code and then allow the vendor-specific driver to produce the final binary representation. There are four major advantages in doing things this way:
1. A software developer can more easily wring compiler errors from the code by having an external compiler that can be run independently from the application.
2. Vendors can still apply their optimization-magic in their device-specific drivers.
3. SPIR-V files can be read at the start of a program and be turned into machine code faster than the original GLSL files could have been turned into machine code.
4. Software developers can distribute their code without having to reveal the shaders’ source code.
Compiler in driver
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18 The new glShaderBinary( ) call replaces both glCreateShader( ) and glCompilerShader( )
Reading SPIR-V-compiled Shaders
FILE *fp = fopen( filename, “r” );
if(fp==NULL) {…}
fseek( fp, 0, SEEK_END );
int numBytes = ftell( fp ); // length of file – guaranteed to be a multiple of 4 GLchar * buffer = new GLchar [numBytes];
rewind( fp ); // same as: “fseek( in, 0, SEEK_SET )” fread( buffer, 1, numBytes, fp );
fclose( fp );
GLuint shaders[2]
glShaderBinary( 2, shaders, GL_SHADER_BINARY_FORMAT_SPIR_V, buffer, numbytes ); GLuint program = glCreateProgram( );
glAttachShader( program, shaders[0] );
glAttachShader( program, shaders[1] );
Computer Graphics
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SPIR-V:
Standard Portable Intermediate Representation for Vulkan
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glslangValidator shaderFile -G [-H] [-I