[2] 立方体(Box)图形的生成算法

顶点数据的生成

 1 bool                        YfBuildBoxVertices
 2 (
 3     Yreal                   extentX,
 4     Yreal                   extentY,  
 5     Yreal                   extentZ, 
 6     YeOriginPose            originPose,
 7     Yuint                   vertexStriding,
 8     Yuint                   vertexPos,
 9     void*                   pVerticesBuffer
10 )
11 {
12     if (!pVerticesBuffer)
13     {
14         return false;
15     }
16 
17     Yuint numVertices = 8;
18 
19     // 顶点赋值
20     char* vertexPtr = (char*)pVerticesBuffer + vertexPos;
21 
22     YsVector3* curVertexPtr   = NULL;
23     YsVector3* curNormalPtr   = NULL;
24     YsVector2* curTexcoordPtr = NULL;
25 
26     Yuint nOffset = 0;
27 
28     YsVector3 vOriginOffset(-extentX / 2, -extentY / 2, -extentZ / 2);
29     if (originPose == YE_ORIGIN_POSE_TOP)
30     {
31         vOriginOffset.y = -extentY;
32     }
33     else if (originPose == YE_ORIGIN_POSE_BOTTOM)
34     {
35         vOriginOffset.y = 0.0f;
36     }
37 
38     for (Yuint k = 0; k < 2; k++)
39     {
40         for (Yuint j = 0; j < 2; j++)
41         {
42             for (Yuint i = 0; i < 2; i++)
43             {
44                 nOffset = (k*4 + j*2 + i) * vertexStriding;
45                 curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
46                 curVertexPtr->x = extentX*i + vOriginOffset.x;
47                 curVertexPtr->z = extentZ*j + vOriginOffset.z;
48                 curVertexPtr->y = extentY*k + vOriginOffset.y;
49             }
50         }
51     }
52 
53     return true;
54 }

三角形索引数据的生成

 1 bool                        YfBuildBoxTriIndices
 2 (
 3     YeIndexType             indexType,
 4     Yuint                   indexStriding,  
 5     Yuint                   indexPos,
 6     void*                   pTriIndicesBuffer
 7 )
 8 {
 9     if (!pTriIndicesBuffer)
10     {
11         return false;
12     }
13 
14     char* indexPtr = (char*)pTriIndicesBuffer + indexPos;
15     if (indexType == YE_INDEX_16_BIT)
16     {
17         YsTriIndex16* triIndexPtr[12];
18         for (Yuint i = 0; i < 12; i++)
19         {
20             triIndexPtr[i] = (YsTriIndex16*)(indexPtr + i * indexStriding);
21         }
22 
23         // bottom
24         triIndexPtr[0]->index0 = 0; triIndexPtr[0]->index1 = 1; triIndexPtr[0]->index2 = 3;
25         triIndexPtr[1]->index0 = 0; triIndexPtr[1]->index1 = 3; triIndexPtr[1]->index2 = 2;
26 
27         // top                                                   
28         triIndexPtr[10]->index0= 4; triIndexPtr[10]->index1= 6; triIndexPtr[10]->index2= 7;
29         triIndexPtr[11]->index0= 4; triIndexPtr[11]->index1= 7; triIndexPtr[11]->index2= 5;
30 
31         // front side
32         triIndexPtr[2]->index0 = 0; triIndexPtr[2]->index1 = 4; triIndexPtr[2]->index2 = 5;
33         triIndexPtr[3]->index0 = 0; triIndexPtr[3]->index1 = 5; triIndexPtr[3]->index2 = 1;
34 
35         // back side
36         triIndexPtr[4]->index0 = 2; triIndexPtr[4]->index1 = 3; triIndexPtr[4]->index2 = 7;
37         triIndexPtr[5]->index0 = 2; triIndexPtr[5]->index1 = 7; triIndexPtr[5]->index2 = 6;
38 
39         // right side
40         triIndexPtr[6]->index0 = 1; triIndexPtr[6]->index1 = 5; triIndexPtr[6]->index2 = 7;
41         triIndexPtr[7]->index0 = 1; triIndexPtr[7]->index1 = 7; triIndexPtr[7]->index2 = 3;
42 
43         // left side                                                       
44         triIndexPtr[8]->index0 = 0; triIndexPtr[8]->index1 = 2; triIndexPtr[8]->index2 = 6;
45         triIndexPtr[9]->index0 = 0; triIndexPtr[9]->index1 = 6; triIndexPtr[9]->index2 = 4;
46     }
47     else
48     {
49         YsTriIndex32* triIndexPtr[12];
50         for (Yuint i = 0; i < 12; i++)
51         {
52             triIndexPtr[i] = (YsTriIndex32*)(indexPtr + i * indexStriding);
53         }
54 
55         // bottom
56         triIndexPtr[0]->index0 = 0; triIndexPtr[0]->index1 = 1; triIndexPtr[0]->index2 = 3;
57         triIndexPtr[1]->index0 = 0; triIndexPtr[1]->index1 = 3; triIndexPtr[1]->index2 = 2;
58 
59         // top                                                   
60         triIndexPtr[10]->index0= 4; triIndexPtr[10]->index1= 6; triIndexPtr[10]->index2= 7;
61         triIndexPtr[11]->index0= 4; triIndexPtr[11]->index1= 7; triIndexPtr[11]->index2= 5;
62 
63         // front side
64         triIndexPtr[2]->index0 = 0; triIndexPtr[2]->index1 = 4; triIndexPtr[2]->index2 = 5;
65         triIndexPtr[3]->index0 = 0; triIndexPtr[3]->index1 = 5; triIndexPtr[3]->index2 = 1;
66 
67         // back side
68         triIndexPtr[4]->index0 = 2; triIndexPtr[4]->index1 = 3; triIndexPtr[4]->index2 = 7;
69         triIndexPtr[5]->index0 = 2; triIndexPtr[5]->index1 = 7; triIndexPtr[5]->index2 = 6;
70 
71         // right side
72         triIndexPtr[6]->index0 = 1; triIndexPtr[6]->index1 = 5; triIndexPtr[6]->index2 = 7;
73         triIndexPtr[7]->index0 = 1; triIndexPtr[7]->index1 = 7; triIndexPtr[7]->index2 = 3;
74 
75         // left side                                                       
76         triIndexPtr[8]->index0 = 0; triIndexPtr[8]->index1 = 2; triIndexPtr[8]->index2 = 6;
77         triIndexPtr[9]->index0 = 0; triIndexPtr[9]->index1 = 6; triIndexPtr[9]->index2 = 4;
78     }
79 
80     return true;
81 }

线框索引数据的生成

 1 bool                        YfBuildBoxWireIndices
 2 (
 3     YeIndexType             indexType,
 4     Yuint                   indexStriding,  
 5     Yuint                   indexPos,
 6     void*                   pWireIndicesBuffer
 7 )
 8 {
 9     if (!pWireIndicesBuffer)
10     {
11         return false;
12     }
13 
14     char* indexPtr = (char*)pWireIndicesBuffer + indexPos;
15     if (indexType == YE_INDEX_16_BIT)
16     {
17         YsLineIndex16* lineIndexPtr[12];
18         for (Yuint i = 0; i < 12; i++)
19         {
20             lineIndexPtr[i] = (YsLineIndex16*)(indexPtr + i * indexStriding);
21         }
22 
23         // bottom
24         lineIndexPtr[0]->index0 = 0; lineIndexPtr[0]->index1 = 1; 
25         lineIndexPtr[1]->index0 = 0; lineIndexPtr[1]->index1 = 2; 
26         lineIndexPtr[2]->index0 = 3; lineIndexPtr[2]->index1 = 1; 
27         lineIndexPtr[3]->index0 = 3; lineIndexPtr[3]->index1 = 2; 
28 
29         // center
30         lineIndexPtr[4]->index0 = 0; lineIndexPtr[4]->index1 = 4; 
31         lineIndexPtr[5]->index0 = 1; lineIndexPtr[5]->index1 = 5; 
32         lineIndexPtr[6]->index0 = 2; lineIndexPtr[6]->index1 = 6; 
33         lineIndexPtr[7]->index0 = 3; lineIndexPtr[7]->index1 = 7; 
34                                         
35         // top                                               
36         lineIndexPtr[8]->index0 = 4; lineIndexPtr[8]->index1 = 5; 
37         lineIndexPtr[9]->index0 = 4; lineIndexPtr[9]->index1 = 6; 
38         lineIndexPtr[10]->index0= 7; lineIndexPtr[10]->index1= 5; 
39         lineIndexPtr[11]->index0= 7; lineIndexPtr[11]->index1= 6;    
40     }
41     else
42     {
43         YsLineIndex32* lineIndexPtr[12];
44         for (Yuint i = 0; i < 12; i++)
45         {
46             lineIndexPtr[i] = (YsLineIndex32*)(indexPtr + i * indexStriding);
47         }
48 
49         // bottom
50         lineIndexPtr[0]->index0 = 0; lineIndexPtr[0]->index1 = 1; 
51         lineIndexPtr[1]->index0 = 0; lineIndexPtr[1]->index1 = 2; 
52         lineIndexPtr[2]->index0 = 3; lineIndexPtr[2]->index1 = 1; 
53         lineIndexPtr[3]->index0 = 3; lineIndexPtr[3]->index1 = 2; 
54 
55         // center
56         lineIndexPtr[4]->index0 = 0; lineIndexPtr[4]->index1 = 4; 
57         lineIndexPtr[5]->index0 = 1; lineIndexPtr[5]->index1 = 5; 
58         lineIndexPtr[6]->index0 = 2; lineIndexPtr[6]->index1 = 6; 
59         lineIndexPtr[7]->index0 = 3; lineIndexPtr[7]->index1 = 7; 
60                                         
61         // top                                               
62         lineIndexPtr[8]->index0 = 4; lineIndexPtr[8]->index1 = 5; 
63         lineIndexPtr[9]->index0 = 4; lineIndexPtr[9]->index1 = 6; 
64         lineIndexPtr[10]->index0= 7; lineIndexPtr[10]->index1= 5; 
65         lineIndexPtr[11]->index0= 7; lineIndexPtr[11]->index1= 6;  
66     }
67 
68     return true;
69 }

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原文地址：https://www.cnblogs.com/WhyEngine/p/3415235.html