A Vertex Buffer Object (VBO) is an OpenGL feature that provides methods for uploading data (vertex, normal vector, color, etc.) to the video device for non-immediate-mode rendering. VBOs offer substantial performance gains over immediate mode rendering primarily because the data resides in the video device memory rather than the system memory and so it can be rendered directly by the video device.
The Vertex Buffer Object specification has been standardized by the OpenGL Architecture Review Board as of OpenGL Version 1.5. Similar functionality was available before the standardization of VBOs via the Nvidia-created extension "Vertex Array Range"[1] or the ATI's "Vertex Array Object"[2] extension.
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The following functions form the core of VBO access and manipulation:
//Initialise VBO - do only once, at start of program //Create a variable to hold the VBO identifier GLuint triangleVBO; //Vertices of a triangle (counter-clockwise winding) float data[] = {1.0, 0.0, 1.0, 0.0, 0.0, -1.0, -1.0, 0.0, 1.0}; //Create a new VBO and use the variable id to store the VBO id glGenBuffers(1, &triangleVBO); //Make the new VBO active glBindBuffer(GL_ARRAY_BUFFER, triangleVBO); //Upload vertex data to the video device glBufferData(GL_ARRAY_BUFFER, sizeof(data), data, GL_STATIC_DRAW); //Draw Triangle from VBO - do each time window, view point or data changes //Establish its 3 coordinates per vertex with zero stride in this array; necessary here glVertexPointer(3, GL_FLOAT, 0, NULL); //Make the new VBO active. Repeat here incase changed since initialisation glBindBuffer(GL_ARRAY_BUFFER, triangleVBO); //Establish array contains vertices (not normals, colours, texture coords etc) glEnableClientState(GL_VERTEX_ARRAY); //Actually draw the triangle, giving the number of vertices provided glDrawArrays(GL_TRIANGLES, 0, sizeof(data) / sizeof(float) / 3); //Force display to be drawn now glFlush();
Function which can read any text or binary file into char buffer:
/* Function will read a text file into allocated char buffer */ char* filetobuf(char *file) { FILE *fptr; long length; char *buf; fptr = fopen(file, "r"); /* Open file for reading */ if (!fptr) /* Return NULL on failure */ return NULL; fseek(fptr, 0, SEEK_END); /* Seek to the end of the file */ length = ftell(fptr); /* Find out how many bytes into the file we are */ buf = malloc(length+1); /* Allocate a buffer for the entire length of the file and a null terminator */ fseek(fptr, 0, SEEK_SET); /* Go back to the beginning of the file */ fread(buf, length, 1, fptr); /* Read the contents of the file in to the buffer */ fclose(fptr); /* Close the file */ buf[length] = 0; /* Null terminator */ return buf; /* Return the buffer */ }
Vertex Shader:
/*----------------- "exampleVertexShader.vert" -----------------*/ #version 150 // Specify which version of GLSL we are using. // in_Position was bound to attribute index 0("shaderAtribute") in vec3 in_Position; void main(void) { gl_Position = vec4(in_Position.x, in_Position.y, in_Position.z, 1.0); } /*--------------------------------------------------------------*/
Fragment Shader:
/*---------------- "exampleFragmentShader.frag" ----------------*/ #version 150 // Specify which version of GLSL we are using. precision highp float; // Video card drivers require this next line to function properly out vec4 fragColor; void main(void) { fragColor = vec4(1.0,1.0,1.0,1.0); //Set colour of each fragment to WHITE } /*--------------------------------------------------------------*/
Main OpenGL Program:
/*--------------------- Main OpenGL Program ---------------------*/ /* Create a variable to hold the VBO identifier */ GLuint triangleVBO; /* This is a handle to the shader program */ GLuint shaderProgram; /* These pointers will receive the contents of our shader source code files */ GLchar *vertexSource, *fragmentSource; /* These are handles used to reference the shaders */ GLuint vertexShader, fragmentShader; const unsigned int shaderAtribute = 0; const float NUM_OF_VERTICES_IN_DATA=3; /* Vertices of a triangle (counter-clockwise winding) */ float data[3][3] = { { 0.0, 1.0, 0.0 }, { -1.0, -1.0, 0.0 }, { 1.0, -1.0, 0.0 } }; /*---------------------- Initialise VBO - (Note: do only once, at start of program) ---------------------*/ /* Create a new VBO and use the variable "triangleVBO" to store the VBO id */ glGenBuffers(1, &triangleVBO); /* Make the new VBO active */ glBindBuffer(GL_ARRAY_BUFFER, triangleVBO); /* Upload vertex data to the video device */ glBufferData(GL_ARRAY_BUFFER, NUM_OF_VERTICES_IN_DATA * 3 * sizeof(float), data, GL_STATIC_DRAW); /* Specify that our coordinate data is going into attribute index 0(shaderAtribute), and contains three floats per vertex */ glVertexAttribPointer(shaderAtribute, 3, GL_FLOAT, GL_FALSE, 0, 0); /* Enable attribute index 0(shaderAtribute) as being used */ glEnableVertexAttribArray(shaderAtribute); /* Make the new VBO active. */ glBindBuffer(GL_ARRAY_BUFFER, triangleVBO); /*-------------------------------------------------------------------------------------------------------*/ /*--------------------- Load Vertex and Fragment shaders from files and compile them --------------------*/ /* Read our shaders into the appropriate buffers */ vertexSource = filetobuf("exampleVertexShader.vert"); fragmentSource = filetobuf("exampleFragmentShader.frag"); /* Assign our handles a "name" to new shader objects */ vertexShader = glCreateShader(GL_VERTEX_SHADER); fragmentShader = glCreateShader(GL_FRAGMENT_SHADER); /* Associate the source code buffers with each handle */ glShaderSource(vertexShader, 1, (const GLchar**)&vertexSource, 0); glShaderSource(fragmentShader, 1, (const GLchar**)&fragmentSource, 0); /* Compile our shader objects */ glCompileShader(vertexShader); glCompileShader(fragmentShader); /*-------------------------------------------------------------------------------------------------------*/ /*-------------------- Create shader program, attach shaders to it and then link it ---------------------*/ /* Assign our program handle a "name" */ shaderProgram = glCreateProgram(); /* Attach our shaders to our program */ glAttachShader(shaderProgram, vertexShader); glAttachShader(shaderProgram, fragmentShader); /* Bind attribute index 0 (shaderAtribute) to in_Position*/ /* "in_Position" will represent "data" array's contents in the vertex shader */ glBindAttribLocation(shaderProgram, shaderAtribute, "in_Position"); /* Link shader program*/ glLinkProgram(shaderProgram); /*-------------------------------------------------------------------------------------------------------*/ /* Set shader program as being actively used */ glUseProgram(shaderProgram); /* Set background colour to BLACK */ glClearColor(0.0, 0.0, 0.0, 1.0); /* Clear background with BLACK colour */ glClear(GL_COLOR_BUFFER_BIT); /* Actually draw the triangle, giving the number of vertices provided by invoke glDrawArrays while telling that our data is a triangle and we want to draw 0-3 vertexes */ glDrawArrays(GL_TRIANGLES, 0, 3); /*---------------------------------------------------------------*/