1 / 20

OpenGl Shaders

OpenGl Shaders. http://www.lighthouse3d.com/tutorials/glsl-tutorial/ 2011 Lighthouse3d.com. What?. GLSL 1.2 - GL Shading Language Cg - Nvidia’s shading language ARB extensions (Architecture Review Board) OpenGL 2.0. PipeLINE overview. Visual Pipeline. Fixed function pipeline.

russ
Download Presentation

OpenGl Shaders

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. OpenGl Shaders • http://www.lighthouse3d.com/tutorials/glsl-tutorial/ • 2011 Lighthouse3d.com

  2. What? • GLSL 1.2 - GL Shading Language • Cg - Nvidia’s shading language • ARB extensions (Architecture Review Board) • OpenGL 2.0

  3. PipeLINE overview

  4. Visual Pipeline

  5. Fixed function pipeline

  6. Fixed v. Programmable • standard OpenGL: Fixed-function pipeline • add more user control & flexibility: programmable • Pipeline processing - 2 stages • vertex processors • fragment processors

  7. Vertex processor • vertex shader executed once for each vertex • vertex position transformation usually using the modelview and projection matrices • normal transformation, normalization • texture coordinate generation and transformation • lighting per vertex • color computation

  8. Fragment processor • fragment - per pixel data • fragment shader executed once for each fragment • computing colors and texture coordinates per pixel • texture application • fog computation • computing normals for lighting per pixel • can discard the fragment or compute color

  9. Setup for GLSL • Each shader like a C module • compiled separately • linked to OpenGL program • example brick shader: ptgmedia.pearsoncmg.com/images/0321334892/samplechapter/rost_ch06.pdf

  10. Process Overview

  11. Creating SHADERs

  12. Process Overview void glShaderSource(GLuint shader, int numOfStrings, const char **strings, int *lenOfStrings); • shader – the handler to the shader. • numOfStrings – the number of strings in the array. • strings – the array of strings. • lenOfStrings – an array with the length of each string, or NULL, meaning that the strings are NULL terminated.

  13. Incorporating shaders

  14. void setShaders() { char *vs,*fs; v = glCreateShader(GL_VERTEX_SHADER); f = glCreateShader(GL_FRAGMENT_SHADER); vs = textFileRead("toon.vert"); fs = textFileRead("toon.frag"); const char * vv = vs; const char * ff = fs; glShaderSource(v, 1, &vv,NULL); glShaderSource(f, 1, &ff,NULL); free(vs);free(fs); glCompileShader(v); glCompileShader(f); p = glCreateProgram(); glAttachShader(p,v); glAttachShader(p,f); glLinkProgram(p); glUseProgram(p); }

  15. Debugging Is hard - no printf - functions to test compilation & linking e.g. void glGetShaderiv(GLuint object, GLenum type, int *param); Can fetch an ‘infoLog’ to get more about errors

  16. GLSL Variables Read-only in shader value set by program Uniform defined for a primitive (outside glBegin-glEnd) not on a per Vertex basis Attribute on a per Vertex basis - for vertex shaders

  17. GLSL Variables bool float int vec{2,3,4} bvec{2,3,4} ivec{2,3,4} const attribute uniform varying mat2 mat3 mat4 sampler{1D,2D,3D,Cube,1DShadow,2DShadow}

  18. GLSL STATEMENTS if - else for loop continue break discard while do-while each shader - one main() declare in / out parameters

  19. Brick VERTEX Shader • uniform vec3 LightPosition; • const float SpecularContribution = 0.3; • const float DiffuseContribution = 1.0 - SpecularContribution; • varying float LightIntensity; • varying vec2 MCposition; • void main() { • vec3 ecPosition = vec3(gl_ModelViewMatrix * gl_Vertex); • vec3 tnorm = normalize(gl_NormalMatrix * gl_Normal); • vec3 lightVec = = normalize(LightPosition - ecPosition); • vec3 reflectVec = reflect(-lightVec, tnorm); • vec3 viewVec = normalize(-ecPosition); • float diffuse = max(dot(lightVec, tnorm), 0.0); • float spec = 0.0; • if (diffuse > 0.0) { • spec = max(dot(reflectVec, viewVec), 0.0); • spec = pow(spec, 16.0); • } • LightIntensity = DiffuseContribution * diffuse + SpecularContribution * spec; • MCposition = gl_Position = gl_Vertex.xy; ftransform(); • }

  20. Brick Fragment Shader uniform vec3 BrickColor, MortarColor; uniform vec2 BrickSize; uniform vec2 BrickPct; varying vec2 MCposition; varying float LightIntensity; void main() { vec3 color; vec2 position, useBrick; position = MCposition / BrickSize; if (fract(position.y * 0.5) > 0.5) position.x += 0.5; position = fract(position); useBrick = step(position, BrickPct); color = mix(MortarColor, BrickColor, useBrick.x * useBrick.y); color *= LightIntensity; gl_FragColor = vec4(color, 1.0); }

More Related