GLSL II Objectives Coupling GLSL to Applications Example

GLSL II

Objectives • Coupling GLSL to Applications • Example applications GLSL 2 2

Linking Shaders to Open. GL • Open. GL Extensions ARB_shader_objects ARB_vertex_shader ARB_fragment_shader • Open. GL 2. 0 Almost identical to using extensions Avoids extension suffixes on function names GLSL 2 3

Program Object • Container for shaders Can contain multiple shaders Other GLSL functions GLuint my. Prog. Obj; my. Prog. Obj = gl. Create. Program(); /* define shader objects here */ gl. Use. Program(my. Prog. Obj); gl. Link. Program(my. Prog. Obj); GLSL 2 4

Reading a Shader • Shader added to program object and compiled • Usual method of passing shader null terminated string using function gl. Shader. Source • If shader in file can write reader to convert file to string GLSL 2 5

Shader Reader #include <stdio. h> char* read. Shader. Source(const char* shader. File) { FILE* fp = fopen(shader. File, "r"); char* buf; long size; if(fp == NULL) return(NULL); fseek(fp, 0 L, SEEK_END); /* end of file */ size = ftell(fp); fseek(fp, )L, SEEK_SET); /* start of file */ GLSL 2 6

Shader Reader (cont) • buf = (char*) malloc(stat. Buf. st_size + 1 * sizeof(char)); fread(buf, 1, size, fp); buf[size] = ''; /null termination */ fclose(fp); return buf; } GLSL 2 7

Adding a Vertex Shader GLint v. Shader; GLunit my. Vertex. Obj; GLchar v. Shaderfile[] = “my_vertex_shader”; GLchar* v. Source = read. Shader. Source(v. Shader. File); gl. Shader. Source(my. Vertex. Obj, 1, &vertex. Shader. File, NULL); my. Vertex. Obj = gl. Create. Shader(GL_VERTEX_SHADER); gl. Compile. Shader(my. Vertex. Obj); gl. Attach. Object(my. Prog. Obj, my. Vertex. Obj); GLSL 2 8

Vertex Attributes • Vertex attributes named in shaders • Linker forms table • Application can get index from table and tie it to application variable • Similar process for uniform variables GLSL 2 9

Vertex Attribute Example GLint color. Attr; color. Attr = gl. Get. Attrib. Location(my. Prog. Obj, "my. Color"); /* my. Color is name in shader */ GLfloat color[4]; gl. Vertex. Attrib 4 fv(color. Attrib, color); /* color is variable in application */ GLSL 2 10

Uniform Variable Example GLint angle. Param; angle. Param = gl. Get. Uniform. Location(my. Prog. Obj, "angle"); /* angle defined in shader */ /* my_angle set in application */ GLfloat my_angle; my_angle = 5. 0 /* or some other value */ gl. Uniform 1 f(angle. Param, my_angle); GLSL 2 11

Vertex Shader Applications • Moving vertices Morphing Wave motion Fractals • Lighting More realistic models Cartoon shaders GLSL 2 12

Wave Motion Vertex Shader • uniform float time; uniform float xs, zs, // frequencies uniform float h; // height scale void main() { vec 4 t = gl_Vertex; t. y = gl_Vertex. y + h*sin(time + xs*gl_Vertex. x) + h*sin(time + zs*gl_Vertex. z); gl_Position = gl_Model. View. Projection. Matrix*t; } GLSL 2 13

Particle System uniform vec 3 init_vel; uniform float g, m, t; void main() { vec 3 object_pos; object_pos. x = gl_Vertex. x + vel. x*t; object_pos. y = gl_Vertex. y + vel. y*t + g/(2. 0*m)*t*t; object_pos. z = gl_Vertex. z + vel. z*t; gl_Position = gl_Model. View. Projection. Matrix* vec 4(object_pos, 1); } GLSL 2 14

Modified Phong Vertex Shader I void main(void) /* modified Phong vertex shader (without distance term) */ { gl_Position = gl_Model. View. Projection. Matrix * gl_Vertex; vec 4 ambient, diffuse, specular; vec 4 eye. Position = gl_Model. View. Matrix * gl_Vertex; vec 4 eye. Light. Pos = gl_Light. Source[0]. position; vec 3 N = normalize(gl_Normal. Matrix * gl_Normal); vec 3 L = normalize(eye. Light. Pos. xyz - eye. Position. xyz); vec 3 E = -normalize(eye. Position. xyz); vec 3 H = normalize(L + E); GLSL 2 15

Modified Phong Vertex Shader II /* compute diffuse, ambient, and specular contributions */ float Kd = max(dot(L, N), 0. 0); float Ks = pow(max(dot(N, H), 0. 0), gl_Front. Material. shininess); float Ka = 0. 0; ambient = Ka*gl_Front. Light. Product[0]. ambient; diffuse = Kd*gl_Front. Light. Product[0]. diffuse; specular = Ks*gl_Front. Light. Product[0]. specular; gl_Front. Color = ambient+diffuse+specular; } GLSL 2 16

Pass Through Fragment Shader /* pass-through fragment shader */ void main(void) { gl_Frag. Color = gl_Color; } GLSL 2 17

Vertex Shader for per Fragment Lighting varying vec 3 N, L, E, H; void main() { gl_Position = gl_Model. View. Projection. Matrix * gl_Vertex; vec 4 eye. Position = gl_Model. View. Matrix * gl_Vertex; vec 4 eye. Light. Pos = gl_Light. Source[0]. position; N = normalize(gl_Normal. Matrix * gl_Normal); L = normalize(eye. Light. Pos. xyz - eye. Position. xyz); E = -normalize(eye. Position. xyz); H = normalize(L + E); } GLSL 2 18

Fragment Shader for Modified Phong Lighting I varying vec 3 N; varying vec 3 L; varying vec 3 E; varying vec 3 H; void main() { vec 3 Normal = normalize(N); vec 3 Light = normalize(L); vec 3 Eye = normalize(E); vec 3 Half = normalize(H); GLSL 2 19

Fragment Shader for Modified Phong Lighting II float Kd = max(dot(Normal, Light), 0. 0); float Ks = pow(max(dot(Half, Normal), 0. 0), gl_Front. Material. shininess); float Ka = 0. 0; vec 4 diffuse = Kd * gl_Front. Light. Product[0]. diffuse; vec 4 specular = Ks * gl_Front. Light. Product[0]. specular; vec 4 ambient = Ka * gl_Front. Light. Product[0]. ambient; gl_Frag. Color = ambient + diffuse + specular; } GLSL 2 20

Vertex vs Fragment Lighting per vertex lighting GLSL 2 per fragment lighting 21

Samplers • Provides access to texture object • Defined for 1, 2, and 3 dimensional textures and for cube maps • In shader: uniform sampler 2 D my. Texture; Vec 2 texcoord; Vec 4 texcolor = texture 2 D(mytexture, texcoord); • In application: tex. Map. Location = gl. Get. Uniform. Location(my. Prog, “my. Texture”); gl. Uniform 1 i(tex. Map. Location, 0); /* assigns to texture unit 0 */ GLSL 2 22

Fragment Shader Applications Texture mapping smooth shading environment mapping GLSL 2 bump mapping 23

Cube Maps • Can form cube map texture by defining six 2 D texture maps correspond to sides of box • Supported by Open. GL • Also supported in GLSL through cubemap sampler vec 4 tex. Color = texture. Cube(mycube, texcoord); • Texture coordinates must be 3 D GLSL 2 24

Environment Map Use reflection vector to locate texture in cube map GLSL 2 25

Environment Maps with Shaders • Environment map usually computed in world coordinates can differ from object coordinates because of modeling matrix May have to keep track of modeling matrix and pass it shader as uniform variable • Can also use reflection map or refraction map (for example to simulate water) GLSL 2 26

Reflection Map Vertex Shader varying vec 3 R; void main(void) { gl_Position = gl_Model. View. Projection. Matrix*gl_Vertex; vec 3 N = normalize(gl_Normal. Matrix*gl_Normal); vec 4 eye. Pos = gl_Model. View. Matrix*gl_Vertex; R = reflect(-eye. Pos. xyz, N); } GLSL 2 27

Refelction Map Fragment Shader varying vec 3 R; uniform sampler. Cube tex. Map; void main(void) { gl_Frag. Color = texture. Cube(tex. Map, R); } GLSL 2 28

Bump Mapping • Perturb normal for each fragment • Store perturbation as textures GLSL 2 29

Normalization Maps • Cube maps can be viewed as lookup tables 1 4 dimensional variables • Vector from origin is pointer into table • Example: store normalized value of vector in map Same for all points on that vector Use “normalization map” instead of normalization function Lookup replaces sqrt, mults and adds GLSL 2 30