As well as colors, normals, and other vertex data PUSHIN’ GEO TO THE GPU JEFF CHASTINE 1

This is what we want to make JEFF CHASTINE 2

Normalized Device Coordinate System (-1, 1) (-1, 0) (-1, -1) (0, 1) (0, -1) (0, 0) (1, 1) (1, 0) (1, -1) JEFF CHASTINE 3

Coordinates of our triangle JEFF CHASTINE 4 (0.0f, 0.5f, 0.0f) (0.5f, -0.5f, 0.0f)(-0.5f, -0.5f, 0.0f)

QUICK! COLOR THEORY! JEFF CHASTINE 5 Represent almost any color by adding red, green and blue Alpha is the transparency Called the primary colors (RGB or RGBA) 0.0 means “all the way off” 1.0 means “all the way on” Examples: Red (1.0, 0.0, 0.0, 1.0) Blue (0.0, 0.0, 1.0, 1.0) Purple (1.0, 0.0, 1.0, 1.0) Yellow (1.0, 1.0, 0.0, 1.0) White (1.0, 1.0, 1.0, 1.0) Black (0.0, 0.0, 0.0, 1.0) Grey (0.5, 0.5, 0.5, 1.0) Brown (0.7, 0.5, 0.1, 1.0)

Colors of our triangle* JEFF CHASTINE 6 (0.0f, 0.0f, 1.0f, 1.0f) (0.0f, 1.0f, 0.0f, 1.0f)(1.0f, 0.0f, 0.0f, 1.0f) *Note the beautiful interpolation of color!

BASIC PROBLEM Get the geometry and color to the GPU Typically also need a normal and texture coordinate for each vertex! Ask the OpenGL driver to create a buffer object This is just a chunk of memory (e.g. array) Nothing to be afraid of! Located on the GPU (probably) JEFF CHASTINE 7

WORKING WITH BUFFERS To create a buffer ID: // This will be the ID of the buffer GLuint buffer; // Ask OpenGL to generate exactly 1 unique ID glGenBuffers(1, &buffer); To set this buffer as the active one and specify which buffer we’re referring to: glBindBuffer(GL_ARRAY_BUFFER, buffer); Notes: That buffer is now bound and active ! Any “drawing” will come from that buffer Any “loading” goes into that buffer JEFF CHASTINE 8

TWO APPROACHES TO LOADING THE BUFFER WITH DATA Assume everything is in GLfloat* (called data ) One-shot call to load the buffer with data: glBufferData(GL_ARRAY_BUFFER, sizeof(data), data, GL_STATIC_DRAW); Other drawing types GL_X_Y: X STREAM for infrequent use and changes STATIC for frequent use and infrequent change DYNAMIC for frequent use and frequent change Y could be DRAW, READ or COPY JEFF CHASTINE 9

HOW WE’LL DO IT Process Create the buffer and pass no data Load the geometry Load the colors (if any) after that Load the normals after that… Note: some like to interlace their vertex data… JEFF CHASTINE 10

A SIDE-BY-SIDE COMPARISON Show the relationship between client code and shader code Assume we’re still trying to draw 1 triangle… numVertices – the number of vertices (will be 3 - duh!) verts – the position information of each vertex (XYZ - array of GLfloats) colors – the color information of each vertex (RGBA - array of GLfloats) JEFF CHASTINE 11

GLuint buffer; glGenBuffers(1, &buffer); buffer Note: buffer “lives” on the graphics card in a nice, two-bedroom loft… JEFF CHASTINE 12

GLuint buffer; glGenBuffers(1, &buffer); glBindBuffer (GL_ARRAY_BUFFER, buffer); buffer Hey – I’m active now JEFF CHASTINE 13

GLuint buffer; glGenBuffers(1, &buffer); glBindBuffer (GL_ARRAY_BUFFER, buffer); glBufferData(GL_ARRAY_BUFFER, numVertices*7*sizeof(GLfloat), NULL, GL_STATIC_DRAW); buffer Now I know how big I am! Where’d the 7 come from? JEFF CHASTINE 14 Allocate how much space (in bytes) we need

GLuint buffer; glGenBuffers(1, &buffer); glBindBuffer (GL_ARRAY_BUFFER, buffer); glBufferData(GL_ARRAY_BUFFER, numVertices*7*sizeof(GLfloat), NULL, GL_STATIC_DRAW); buffer Now I know how big I am! JEFF CHASTINE 15 (x, y, z) + (r, g, b, a) = 7 Where’d the 7 come from? Allocate how much space (in bytes) we need

GLuint buffer; glGenBuffers(1, &buffer); glBindBuffer (GL_ARRAY_BUFFER, buffer); glBufferData(GL_ARRAY_BUFFER, numVertices*7*sizeof(GLfloat), NULL, GL_STATIC_DRAW); glBufferSubData (GL_ARRAY_BUFFER, 0, numVertices*3*sizeof(GLfloat), verts); glBufferSubData (GL_ARRAY_BUFFER, numVertices*3*sizeof(GLfloat), numVertices*4*sizeof(GLfloat), colors); buffer Now I’m putting verts at the beginning verts Put verts at 0… it’s pretty big though… JEFF CHASTINE 16

GLuint buffer; glGenBuffers(1, &buffer); glBindBuffer (GL_ARRAY_BUFFER, buffer); glBufferData(GL_ARRAY_BUFFER, numVertices*7*sizeof(GLfloat), NULL, GL_STATIC_DRAW); glBufferSubData (GL_ARRAY_BUFFER, 0, numVertices*3*sizeof(GLfloat), verts); glBufferSubData (GL_ARRAY_BUFFER, numVertices*3*sizeof(GLfloat), numVertices*4*sizeof(GLfloat), colors); buffer I’m putting colors next verts Put colors starting right after that! It’s pretty big too… colors JEFF CHASTINE 17

WHAT WE HAVE SO FAR… We have a buffer with an ID That buffer lives on the graphics card That buffer is full of vertex position/color data How do we get that info to our shader? JEFF CHASTINE 18

HOW TO LINK TO THE SHADER Query the shader program for its variables The code below goes into the shader program and gets the “vPosition” ID GLuint vpos; vpos = glGetAttribLocation (programID, “vPosition”); In OpenGL, we have to enable things (attributes, in this case): glEnableVertexAttribArray(vpos); // turn on vPosition Finally, we set the location and tell it the format of the data in the buffer glVertexAttribPointer(vpos, 3, GL_FLOAT, GL_FALSE, 0, 0); void glVertexAttribPointer(GLuint index, GLint size, Glenum type, GLboolean normalized, GLsizei stride, const GLvoid* offset ); JEFF CHASTINE 19

GLuint loc = glGetAttribLocation(shaderProgramID, "vPosition"); #version 130 in vec4 vPosition; in vec4 vColor; out vec4 color; void main () { color = vColor; gl_Position = vPosition; } Find the variable “vPosition” inside the shader JEFF CHASTINE 20

GLuint loc = glGetAttribLocation(shaderProgramID, "vPosition"); glEnableVertexAttribArray(loc); glVertexAttribPointer(loc, 3, GL_FLOAT, GL_FALSE, 0, 0); #version 130 in vec4 vPosition; in vec4 vColor; out vec4 color; void main () { color = vColor; gl_Position = vPosition; } buffer Guys! I’m still active, remember? verts colors JEFF CHASTINE 21

GLuint loc2 = glGetAttribLocation(shaderProgramID, "vColor"); glEnableVertexAttribArray(loc2); glVertexAttribPointer(loc2, 4, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(numVertices*3*sizeof(GLfloat))); #version 130 in vec4 vPosition; in vec4 vColor; out vec4 color; void main () { color = vColor; gl_Position = vPosition; } buffer Tell vColor where to find its data in me… verts colors JEFF CHASTINE 22

GLuint loc = glGetAttribLocation(shaderProgramID, "vPosition"); glEnableVertexAttribArray(loc); glVertexAttribPointer(loc, 3, GL_FLOAT, GL_FALSE, 0, 0); GLuint loc2 = glGetAttribLocation(shaderProgramID, "vColor"); glEnableVertexAttribArray(loc2); glVertexAttribPointer(loc2, 4, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(numVertices*3*sizeof(GLfloat))); #version 130 in vec4 vPosition; in vec4 vColor; out vec4 color; void main () { color = vColor; gl_Position = vPosition; } JEFF CHASTINE 23

ONE LAST THING Vertex Array Objects (VAOs) “Pure State” - it remembers almost everything about buffers Set it up once, then just call it before drawing! glVertexAttribPointer… Doesn’t bind the VBO though… Creating a vertex array object: // This will be the ID of the VAO GLuint vao; // Ask the driver for exactly 1 unique ID glGenVertexArrays(1, &vao); // Everything after this will be part of the VAO glBindVertexArray(vao); JEFF CHASTINE 24

// Create the "remember all" glGenVertexArrays(1, &vao); glBindVertexArray(vao); // Create a buffer and bind it as active glGenBuffers(1, &vbo); glBindBuffer(GL_ARRAY_BUFFER, vbo); // Create space and load the buffer glBufferData(GL_ARRAY_BUFFER, 7*3*sizeof(GLfloat), NULL, GL_STATIC_DRAW); glBufferSubData(GL_ARRAY_BUFFER, 0, 3*3*sizeof(GLfloat), vertices); glBufferSubData(GL_ARRAY_BUFFER, 3*3*sizeof(GLfloat),3*4*sizeof(GLfloat), colors); // Find the positions of the variables in the shader positionID = glGetAttribLocation(shaderProgramID, "vPosition"); colorID = glGetAttribLocation(shaderProgramID, "vColor"); // Tell the shader variables where to find their data glVertexAttribPointer(positionID, 3, GL_FLOAT, GL_FALSE, 0, 0); glVertexAttribPointer(colorID, 4, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(3*3*sizeof(GLfloat))); glUseProgram(shaderProgramID); glEnableVertexAttribArray(positionID); glEnableVertexAttribArray(colorID); JEFF CHASTINE 25

END WITH A UTAH TEAPOT! JEFF CHASTINE 26