現在、OpenGL、Cg、およびC ++を使用して直接レイキャスティングボリュームレンダリングを実装するようにコーディングしています。コンピューターのシステムはWin7で、グラフィックスはnVidiaGTX570です。
実際、直接レイキャスティングボリュームレンダリングの基本機能を正常に実装しましたが、ここで照明を追加したいので、ローカル照明モデルを使用します。イルミネーション用のコードを数行追加すると、Cgコンパイラエラーが発生します。追加する前は、正常に動作します。
私が使用するCgプロファイルはCG_PROFILE_VP40とCG_PROFILE_FP40です。
今私は私のCgコードを投稿します：
#define kNumberOfRaySteps 800
// Define interface between the application and the vertex program
struct app_vertex
{
float4 Position : POSITION;
float4 TexCoord : TEXCOORD1;
float4 Color : COLOR0;
};
// Define the interface between the vertex- and the fragment programs
struct vertex_fragment
{
float4 Position : POSITION; // For the rasterizer
float4 TexCoord : TEXCOORD0;
float4 Color : TEXCOORD1;
float4 Pos : TEXCOORD2;
};
struct fragment_out
{
float4 Color : COLOR0;
};
//Blinn-Phong illumination
float3 shading(float3 N, float3 V, float3 L) {
// material properties
float3 Ka = float3(0.1, 0.1, 0.1); // ambient
float3 Kd = float3(0.6, 0.6, 0.6); // diffuse
float3 Ks = float3(0.2, 0.2, 0.2); // specular
float n = 100.0; // shininess
// light properties
float3 lightColor = float3(1.0, 1.0, 1.0);
float3 ambientLight = float3(0.3, 0.3, 0.3);
// Calculate halfway vector
float3 H= normalize(L + V);
// Compute ambient term
float3 ambient = Ka * ambientLight;
// Compute the diffuse term
float diffuseLight = max(dot(L, N), 0);
float3 diffuse = Kd * lightColor * diffuseLight;
// Compute the specular term
float specularLight = pow(max(dot(H, N), 0), n);
if (diffuseLight <= 0) specularLight = 0;
float3 specular = Ks * lightColor * specularLight;
return ambient + diffuse + specular;
}
// Raycasting vertex program implementation
vertex_fragment vertex_main( app_vertex IN )
{
vertex_fragment OUT;
// Get OpenGL state matrices
float4x4 ModelView = glstate.matrix.modelview[0];//model view matrix 0
float4x4 ModelViewProj = glstate.matrix.mvp;//modelview-projection matrix
// Transform vertex
OUT.Position = mul( ModelViewProj, IN.Position );
OUT.Pos = mul( ModelViewProj, IN.Position );
OUT.TexCoord = IN.TexCoord;
OUT.Color = IN.Color;
return OUT;
}
// Raycasting fragment program implementation
fragment_out fragment_main( vertex_fragment IN,
uniform sampler2D tex, //back face
uniform sampler2D preint_table,//pre-intergration classification
uniform sampler3D volume_tex, //volume data
uniform float stepsize,
//add local illumination
uniform float3 lightPosition,//the external light position
uniform float3 eyePosition,//the eye position
uniform sampler3D normal_vec//normal vectors
)
{
fragment_out OUT;
// find the right place to lookup in the backside buffer
//normalize the spatial position to range [0,1]
float2 texc = ((IN.Pos.xy / IN.Pos.w) + 1) / 2;
// the start position of the ray is stored in the texturecoordinate
float4 start = IN.TexCoord;
float4 back_position = tex2D(tex, texc);
float3 dir = float3(0,0,0);
dir.x = back_position.x - start.x;
dir.y = back_position.y - start.y;
dir.z = back_position.z - start.z;
// the length from front to back is calculated and used to terminate the ray
float len = length(dir.xyz);
float3 norm_dir = normalize(dir);
float delta = stepsize;
float3 delta_dir = norm_dir * delta;
float delta_dir_len = length(delta_dir);
float3 vec1 = start.xyz;//position of back point
float3 vec2 = start.xyz;//position of front point
float4 col_acc = float4(0,0,0,0);
float alpha_acc = 0;//accumulation of alpha value(opacity)
float length_acc = 0;
float4 color_sample;
float alpha_sample;
float4 lookup = float4(0.0,0.0,0.0,0.0);
//set background color to blue
float4 backgroundColor = float4(1.0,1.0,1.0,0.0);
//loops:sample points
for(int i = 0; i < kNumberOfRaySteps; i++)
{
vec2 += delta_dir;
lookup.x = (tex3D(volume_tex,vec1)).x;//scalar value of back point
lookup.y = (tex3D(volume_tex,vec2)).x;//scalar value of front point
color_sample = tex2D(preint_table,lookup.xy);
alpha_sample = color_sample.a;
//add code for illumination
float3 N = tex3D(normal_vec,start.xyz).xyz;//normal vector
//calculate light and viewing directions
float3 L = normalize(lightPosition - IN.Position.xyz);
float3 V = normalize(eyePosition - IN.Position.xyz);
col_acc += (1.0 - alpha_acc) * color_sample * alpha_sample * 2;
//add ilumination color
col_acc += float4(shading(N,V,L),0.0);
alpha_acc += (1.0 - alpha_acc) * alpha_sample;
vec1 += delta_dir;//next sample point
length_acc += delta_dir_len;//accumulation of ray length in the cube
//change the background color from black to other color
if(length_acc >= len)
col_acc += (1.0 - alpha_acc) * backgroundColor;
// terminate if opacity > 1 or the ray is outside the volume
if(length_acc >= len || alpha_acc > 0.99) break;
}
OUT.Color = col_acc;
return OUT;
}
Cgエラーに関する情報：
線を消せば
col_acc += float4(shading(N,V,L),0.0);
そうすればプログラムはうまく動きます、確かに私は照明効果を得ることができません。ですから、照明効果を計算する関数の陰影に何か問題があると思います。
しかし、私はそれを理解することはできません。誰かがこの問題を解決する方法を教えてもらえますか？