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Introduction to Shaders

Introduction to Shaders. Quick Background. A vertex is a 3D point ( x , y , z ) A triangle is made from 3 vertices h as a normal Note: vertices can have normals too!. Quick Background. Models/Meshes are made from triangles OpenGL doesn’t support Quads (4 vertices).

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Introduction to Shaders

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  1. Introduction to Shaders Jeff Chastine

  2. Quick Background • A vertex is a 3D point (x, y, z) • A triangle • is made from 3 vertices • has a normal • Note: vertices can have normals too! Jeff Chastine

  3. Quick Background • Models/Meshes are made from triangles • OpenGL doesn’t support Quads (4 vertices) Jeff Chastine

  4. Quick Background • Hardware has changed! • Was “fixed” • More of the graphics pipeline is programmable • OpenGL has changed! • Was “fixed” • Is now shader-based Jeff Chastine

  5. Intro to Shaders • A shader is a program • Has source code (text file) • Cg, HLSL and GLSL • GLSL is very “C-like” • Is compiled into a program • We get back IDs, which are just ints! Jeff Chastine

  6. Intro to Shaders • Two primary types of shaders: • Vertex shader • Changes the position of a vertex (trans/rot/skew) • May determine color of the vertex • Fragment shader • Determines the color of a pixel • Uses lighting, materials, normals, etc… Jeff Chastine

  7. Making a Shader Program • Compile a vertex shader (get an ID) • Compile a fragment shader (get an ID) • Check for compilation errors • Link those two shaders together (get an ID) • Keep that ID! • Use that ID before you render triangles • Can have separate shaders for each model Jeff Chastine

  8. Examples in vec4 s_vPosition; void main () { // Look, Ma! I avoided any matrix multiplication! // The value of s_vPosition should be between -1.0 and +1.0 gl_Position = s_vPosition; } --------------------------------------------------------------------- out vec4 s_vColor; void main () { // No matter what, color the pixel red! fColor = vec4 (1.0, 0.0, 0.0, 1.0); } Jeff Chastine

  9. Compiling Vertex and Fragment Shaders • <GLuint> glCreateShader (<type>) • Creates an ID (a GLuint) of a shader • Example: GLuint ID = glCreateShader(GL_VERTEX_SHADER); • glShaderSource (<id>, <count>, <src code>, <lengths>) • Binds the source code to the shader • Happens before compilation • glCompileShader (<id>) • Used to make part the shader program Jeff Chastine

  10. Creating/Linking/Using the Shader • <GLuint> glCreateProgram() • Returns an ID – keep this for the life of the program • glAttachShader(<prog ID>, <shader ID>) • Do this for both the vertex and fragment shaders • glLinkProgram(<prog ID>) • Actually makes the shader program • glUseProgram(<prog ID>) • Use this shader when you’re about to draw triangles Jeff Chastine

  11. END WITH A DRAGON! Jeff Chastine

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