//******************************************************************
//
// OpenGL ES 2.0 vertex shader that implements the following
// OpenGL ES 1.1 fixed function pipeline
//
// - compute lighting equation for up to eight directional/point/
// - spot lights
// - transform position to clip coordinates
// - texture coordinate transforms for up to two texture coordinates
// - compute fog factor
// - compute user clip plane dot product (stored as v_ucp_factor)
//
//******************************************************************
#define NUM_TEXTURES 2
#define GLI_FOG_MODE_LINEAR 0
#define GLI_FOG_MODE_EXP 1
#define GLI_FOG_MODE_EXP2 2
struct light {
vec4 position; // light position for a point/spot light or
// normalized dir. for a directional light
vec4 ambient_color;
vec4 diffuse_color;
vec4 specular_color;
vec3 spot_direction;
vec3 attenuation_factors;
float spot_exponent;
float spot_cutoff_angle;
bool compute_distance_attenuation;
};
struct material {
vec4 ambient_color;
vec4 diffuse_color;
vec4 specular_color;
vec4 emissive_color;
float specular_exponent;
};
const float c_zero = 0.0;
const float c_one = 1.0;
const int indx_zero = 0;
const int indx_one = 1;
uniform mat4 mvp_matrix; // combined model-view + projection matrix
uniform mat4 modelview_matrix; // model view matrix
uniform mat3 inv_modelview_matrix; // inverse model-view
// matrix used
// to transform normal
uniform mat4 tex_matrix[NUM_TEXTURES]; // texture matrices
uniform bool enable_tex[NUM_TEXTURES]; // texture enables
uniform bool enable_tex_matrix[NUM_TEXTURES]; // texture matrix enables
uniform material material_state;
uniform vec4 ambient_scene_color;
uniform light light_state[8];
uniform bool light_enable_state[8]; // booleans to indicate which of eight
// lights are enabled
uniform int num_lights; // number of lights enabled = sum of
// light_enable_state bools set to TRUE
uniform bool enable_lighting; // is lighting enabled
uniform bool light_model_two_sided; // is two-sided lighting enabled
uniform bool enable_color_material; // is color material enabled
uniform bool enable_fog; // is fog enabled
uniform float fog_density;
uniform float fog_start, fog_end;
uniform int fog_mode; // fog mode - linear, exp, or exp2
uniform bool xform_eye_p; // xform_eye_p is set if we need
// Peye for user clip plane,
// lighting, or fog
uniform bool rescale_normal; // is rescale normal enabled
uniform bool normalize_normal; // is normalize normal enabled
uniform float rescale_normal_factor; // rescale normal factor if
// glEnable(GL_RESCALE_NORMAL)
uniform vec4 ucp_eqn; // user clip plane equation –
// - one user clip plane specified
uniform bool enable_ucp; // is user clip plane enabled
//******************************************************
// vertex attributes - not all of them may be passed in
//******************************************************
attribute vec4 a_position; // this attribute is always specified
attribute vec4 a_texcoord0;// available if enable_tex[0] is true
attribute vec4 a_texcoord1;// available if enable_tex[1] is true
attribute vec4 a_color; // available if !enable_lighting or
// (enable_lighting && enable_color_material)
attribute vec3 a_normal; // available if xform_normal is set
// (required for lighting)
//************************************************
// varying variables output by the vertex shader
//************************************************
varying vec4 v_texcoord[NUM_TEXTURES];
varying vec4 v_front_color;
varying vec4 v_back_color;
varying float v_fog_factor;
varying float v_ucp_factor;
//************************************************
// temporary variables used by the vertex shader
//************************************************
vec4 p_eye;
vec3 n;
vec4 mat_ambient_color;
vec4 mat_diffuse_color;
vec4
lighting_equation(int i)
{
vec4 computed_color = vec4(c_zero, c_zero, c_zero, c_zero);
vec3 h_vec;
float ndotl, ndoth;
float att_factor;
att_factor = c_one;
if(light_state[i].position.w != c_zero)
{
float spot_factor;
vec3 att_dist;
vec3 VPpli;
// this is a point or spot light
// we assume "w" values for PPli and V are the same
VPpli = light_state[i].position.xyz - p_eye.xyz;
if(light_state[i].compute_distance_attenuation)
{
// compute distance attenuation
att_dist.x = c_one;
att_dist.z = dot(VPpli, VPpli);
att_dist.y = sqrt(att_dist.z);
att_factor = c_one / dot(att_dist,
light_state[i].attenuation_factors);
}
VPpli = normalize(VPpli);
if(light_state[i].spot_cutoff_angle < 180.0)
{
// compute spot factor
spot_factor = dot(-VPpli, light_state[i].spot_direction);
if(spot_factor >= cos(radians(light_state[i].spot_cutoff_angle)))
{
spot_factor = pow(spot_factor,light_state[i].spot_exponent);
}
else{
spot_factor = c_zero;
}
att_factor *= spot_factor;
}
}
else
{
// directional light
VPpli = light_state[i].position.xyz;
}
if(att_factor > c_zero)
{
// process lighting equation --> compute the light color
computed_color += (light_state[i].ambient_color * mat_ambient_color);
ndotl = max(c_zero, dot(n, VPpli));
computed_color += (ndotl * light_state[i].diffuse_color * mat_diffuse_color);
h_vec = normalize(VPpli + vec3(c_zero, c_zero, c_one));
ndoth = dot(n, h_vec);
if (ndoth > c_zero)
{
computed_color += (pow(ndoth,material_state.specular_exponent) *
material_state.specular_color *
light_state[i].specular_color);
}
computed_color *= att_factor; // multiply color with
// computed attenuation factor
// * computed spot factor
}
return computed_color;
}
float compute_fog()
{
float f;
// use eye Z as approximation
if(fog_mode == GLI_FOG_MODE_LINEAR)
{
f = (fog_end - p_eye.z) / (fog_end - fog_start);
}
else if(fog_mode == GLI_FOG_MODE_EXP)
{
f = exp(-(p_eye.z * fog_density));
}
else
{
f = (p_eye.z * fog_density);
f = exp(-(f * f));
}
f = clamp(f, c_zero, c_one);
return f;
}
vec4 do_lighting()
{
vec4 vtx_color;
int i, j;
vtx_color = material_state.emissive_color +
(mat_ambient_color * ambient_scene_color);
j = (int)c_zero;
for (i=(int)c_zero; i<8; i++)
{
if(j >= num_lights)
break;
if (light_enable_state[i])
{
j++;
vtx_color += lighting_equation(i);
}
}
vtx_color.a = mat_diffuse_color.a;
return vtx_color;
}
void main(void)
{
int i, j;
// do we need to transform P
if(xform_eye_p)
p_eye = modelview_matrix * a_position;
if(enable_lighting)
{
n = inv_modelview_matrix * a_normal;
if(rescale_normal)
n = rescale_normal_factor * n;
if (normalize_normal)
n = normalize(n);
mat_ambient_color = enable_color_material ? a_color
: material_state.ambient_color;
mat_diffuse_color = enable_color_material ? a_color
: material_state.diffuse_color;
v_front_color = do_lighting();
v_back_color = v_front_color;
// do 2-sided lighting
if(light_model_two_sided)
{
n = -n;
v_back_color = do_lighting();
}
}
else
{
// set the default output color to be the per-vertex /
// per-primitive color
v_front_color = a_color;
v_back_color = a_color;
}
// do texture xforms
v_texcoord[indx_zero] = vec4(c_zero, c_zero, c_zero, c_one);
if(enable_tex[indx_zero])
{
if(enable_tex_matrix[indx_zero])
v_texcoord[indx_zero] = tex_matrix[indx_zero] * a_texcoord0;
else
v_texcoord[indx_zero] = a_texcoord0;
}
v_texcoord[indx_one] = vec4(c_zero, c_zero, c_zero, c_one);
if(enable_tex[indx_one])
{
if(enable_tex_matrix[indx_one])
v_texcoord[indx_one] = tex_matrix[indx_one] * a_texcoord1;
else
v_texcoord[indx_one] = a_texcoord1;
}
v_ucp_factor = enable_ucp ? dot(p_eye, ucp_eqn) : c_zero;
v_fog_factor = enable_fog ? compute_fog() : c_one;
gl_Position = mvp_matrix * a_position;
}
在三維中常常需要重算正交的基向量組,
由于叉乘操作是有序的. 一般來說 : UxV不等于VxU,
所有往往記不住到底是哪個左向量乘哪個右向量求出
第三個向量,由于吃了一些虧所以做了總結(jié).
i,j,k三個基向量, 如果你使用的圖形引擎Z往屏幕外面,
右手邊X和上方向Y規(guī)定為正方向的一組正交向量,如果
你使用的模型的基向量組和它相同,那么放心用.
ix
j=k, kx
i=j, jx
k=i 但是你可能不總是那么幸運(yùn).也許你打算使用Z往屏幕里面,
右手邊X和上方向Y規(guī)定為正方向的一組正交向量,這時你就
需要改變叉乘方式了
jx
i=k, ix
k=j, kx
j=i
也就是統(tǒng)統(tǒng)反過來使用就可以了.
但是如果你想使用Z往屏幕里面,右手邊X和下方向Y規(guī)定
為正方向的一組正交向量時這時你又需要怎么弄呢?
其實(shí)還是:
ix
j=k, kx
i=j, jx
k=i 如果你想使用Z往屏幕里面,左手邊X和下方向Y規(guī)定
為正方向的一組正交向量時這時你又需要怎么弄呢?
這時又是:
jx
i=k, ix
k=j, kx
j=i
也是統(tǒng)統(tǒng)反過來使用.
這時怎么得到得結(jié)論?
其實(shí)就是通過計(jì)算得到的
以下都假設(shè)x右為正方向,y上為正方向,z往屏幕外為正方向設(shè)備的環(huán)境
測試.
var vec3 = glMatrix.vec3;
console.log("-------------------->z軸往屏幕里為正的坐標(biāo)系");
var u = vec3.fromValues(1,0,0)
var v = vec3.fromValues(0,1,0)
var w = vec3.fromValues(0,0,-1)
console.log(vec3.cross(vec3.create(), w,v));
console.log(vec3.cross(vec3.create(), u,w));
console.log(vec3.cross(vec3.create(), v,u));
console.log("-------------------->y軸向下為正的坐標(biāo)系");
var u = vec3.fromValues(1,0,0)
var v = vec3.fromValues(0,-1,0)
var w = vec3.fromValues(0,0,1)
console.log(vec3.cross(vec3.create(), w,v));
console.log(vec3.cross(vec3.create(), u,w));
console.log(vec3.cross(vec3.create(), v,u));
console.log("-------------------->x軸向左為正的坐標(biāo)系");
var u = vec3.fromValues(-1,0,0)
var v = vec3.fromValues(0,1,0)
var w = vec3.fromValues(0,0,1)
console.log(vec3.cross(vec3.create(), w,v));
console.log(vec3.cross(vec3.create(), u,w));
console.log(vec3.cross(vec3.create(), v,u));
console.log("-------------------->全部反為正坐標(biāo)系");
var u = vec3.fromValues(-1,0,0)
var v = vec3.fromValues(0,-1,0)
var w = vec3.fromValues(0,0,-1)
console.log(vec3.cross(vec3.create(), w,v));
console.log(vec3.cross(vec3.create(), u,w));
console.log(vec3.cross(vec3.create(), v,u));
以上都能得到正確的向量組
console.log("-------------------->z軸往屏幕外為正坐標(biāo)系");
var u = vec3.fromValues(1,0,0)
var v = vec3.fromValues(0,1,0)
var w = vec3.fromValues(0,0,1)
console.log(vec3.cross(vec3.create(), v,w));
console.log(vec3.cross(vec3.create(), w,u));
console.log(vec3.cross(vec3.create(), u,v));
console.log("-------------------->任意兩個是為負(fù)數(shù)的坐標(biāo)系");
var u = vec3.fromValues(-1,0,0)
var v = vec3.fromValues(0,1,0)
var w = vec3.fromValues(0,0,-1)
console.log(vec3.cross(vec3.create(), v,w));
console.log(vec3.cross(vec3.create(), w,u));
console.log(vec3.cross(vec3.create(), u,v));
以上也都能得到正確的向量組.
結(jié)論就是如果偶數(shù)相反就正常使用,如果是奇數(shù)相反就
用反過來用.