小贝子编程

OpenGLES排序顶点以使用glDrawArrays绘制正确的形状



我正在学习OpenGLES 2.0教程，作者在教程中渲染了一个带有纹理的球体。该球体看起来很好，是从Wavefront OBJ文件生成的。他使用的标题看起来像：

/*
created with obj2opengl.pl
source file    : sphere.obj
vertices       : 326
faces          : 648
normals        : 326
texture coords : 390
*/
unsigned int sphereNumVerts = 1944;
float sphereVerts [] = {
// f 28/1/1 1/2/2 21/3/3
7.6687116638888e-09, 0.466097, 0.115308018404908,
-0.0265919923312883, 0.466097, 0.112200018404908,
7.6687116638888e-09, 0.4795745, 1.84049079729628e-08,
// f 21/4/3 1/2/2 2/5/4
7.6687116638888e-09, 0.4795745, 1.84049079729628e-08,
-0.0265919923312883, 0.466097, 0.112200018404908,
-0.0517499923312883, 0.466097, 0.103043018404908,
// f 21/6/3 2/5/4 3/7/5
7.6687116638888e-09, 0.4795745, 1.84049079729628e-08,
-0.0517499923312883, 0.466097, 0.103043018404908,
-0.0741184923312883, 0.466097, 0.088331018404908,
... TRUNCATED ...
// f 326/388/326 323/361/324 322/360/323
7.6687116638888e-09, -0.5204255, 1.84049079729628e-08,
0.0767490076687117, -0.490272, 0.152820018404908,
0.109923007668712, -0.490272, 0.131001518404908,
// f 326/389/326 324/362/325 323/361/324
7.6687116638888e-09, -0.5204255, 1.84049079729628e-08,
0.0394375076687117, -0.490272, 0.166400518404908,
0.0767490076687117, -0.490272, 0.152820018404908,
// f 326/390/326 325/363/299 324/362/325
7.6687116638888e-09, -0.5204255, 1.84049079729628e-08,
7.6687116638888e-09, -0.490272, 0.171010018404908,
0.0394375076687117, -0.490272, 0.166400518404908,
};
float sphereNormals [] = {
// f 28/1/1 1/2/2 21/3/3
-0.00802618948953466, 0.967367838494132, 0.253248978930753,
-0.0662268425664943, 0.967371914269316, 0.244551803932402,
0, 1, -0,
// f 21/4/3 1/2/2 2/5/4
0, 1, -0,
-0.0662268425664943, 0.967371914269316, 0.244551803932402,
-0.120826192029109, 0.967370556337772, 0.222699883364347,
// f 21/6/3 2/5/4 3/7/5
0, 1, -0,
-0.120826192029109, 0.967370556337772, 0.222699883364347,
-0.168924852220773, 0.967372786949467, 0.18882342379009,
// f 21/8/3 3/7/5 4/9/6
... TRUNCATED ...
0, -1, -0,
0.163004478217867, -0.939604578019474, 0.300953114364626,
0.22801091084251, -0.939601478627697, 0.255264736885873,
// f 326/389/326 324/362/325 323/361/324
0, -1, -0,
0.0891781381121659, -0.939606064036581, 0.330435627783284,
0.163004478217867, -0.939604578019474, 0.300953114364626,
// f 326/390/326 325/363/299 324/362/325
0, -1, -0,
0.0105903724426618, -0.939606044104724, 0.342094030777207,
0.0891781381121659, -0.939606064036581, 0.330435627783284,
};
float sphereTexCoords [] = {
// f 28/1/1 1/2/2 21/3/3
0.000000, 0.925926,
0.037037, 0.925926,
0.000000, 1.000000,
// f 21/4/3 1/2/2 2/5/4
0.037037, 1.000000,
0.037037, 0.925926,
0.074074, 0.925926,
// f 21/6/3 2/5/4 3/7/5
0.074074, 1.000000,
0.074074, 0.925926,
0.111111, 0.925926,
... TRUNCATED ...
// f 326/388/326 323/361/324 322/360/323
0.888889, 0.037037,
0.925926, 0.111111,
0.888889, 0.111111,
// f 326/389/326 324/362/325 323/361/324
0.925926, 0.037037,
0.962963, 0.111111,
0.925926, 0.111111,
// f 326/390/326 325/363/299 324/362/325
0.962963, 0.037037,
1.000000, 0.111111,
0.962963, 0.111111,
};

我制作了我自己的对象，并使用Cheetah3D将其导出到一个头文件中，它看起来像这样：

// Headerfile *.h (generated by Cheetah3D)
//
// There are the following name conventions:
//  NAME            =name of the object in Cheetah3D. Caution!! Avoid giving two objects the same name
//  NAME_vertex     =float array which contains the vertex,normal and uvcoord data 
//  NAME_index      =int array which contains the polygon index data
//  NAME_vertexcount    =number of vertices
//  NAME_polygoncount   =number of triangles
//
// The vertex data is saved in the following format:
//  u0,v0,normalx0,normaly0,normalz0,x0,y0,z0
//  u1,v1,normalx1,normaly1,normalz1,x1,y1,z1
//  u2,v2,normalx2,normaly2,normalz2,x2,y2,z2
//  ...
// You can draw the mesh the following way:
//  glEnableClientState(GL_INDEX_ARRAY);
//  glEnableClientState(GL_NORMAL_ARRAY);
//  glEnableClientState(GL_VERTEX_ARRAY);
//  glEnableClientState(GL_TEXTURE_COORD_ARRAY);
//  glInterleavedArrays(GL_T2F_N3F_V3F,0,NAME_vertex);
//  glDrawElements(GL_TRIANGLES,NAME_polygoncount*3,GL_UNSIGNED_INT,NAME_index);
//
#define Box_vertexcount     24
#define Box_polygoncount    12

float Box_vertex[Box_vertexcount][8]={
{0.00000, 1.00000, 0.00000, 0.00000, 1.00000, -0.15000, -0.15000, 0.15000},
{0.00000, 0.00000, 0.00000, 0.00000, 1.00000, -0.15000, 0.15000, 0.15000},
{1.00000, 0.00000, 0.00000, 0.00000, 1.00000, 0.15000, 0.15000, 0.15000},
{1.00000, 1.00000, 0.00000, 0.00000, 1.00000, 0.15000, -0.15000, 0.15000},
{0.00000, 1.00000, 0.00000, 0.00000, -1.00000, 0.15000, -0.15000, -0.15000},
{0.00000, 0.00000, 0.00000, 0.00000, -1.00000, 0.15000, 0.15000, -0.15000},
{1.00000, 0.00000, 0.00000, 0.00000, -1.00000, -0.15000, 0.15000, -0.15000},
{1.00000, 1.00000, 0.00000, 0.00000, -1.00000, -0.15000, -0.15000, -0.15000},
{0.00000, 1.00000, -1.00000, 0.00000, 0.00000, -0.15000, -0.15000, -0.15000},
{0.00000, 0.00000, -1.00000, 0.00000, 0.00000, -0.15000, 0.15000, -0.15000},
{1.00000, 0.00000, -1.00000, 0.00000, 0.00000, -0.15000, 0.15000, 0.15000},
{1.00000, 1.00000, -1.00000, 0.00000, 0.00000, -0.15000, -0.15000, 0.15000},
{0.00000, 1.00000, 1.00000, 0.00000, 0.00000, 0.15000, -0.15000, 0.15000},
{0.00000, 0.00000, 1.00000, 0.00000, 0.00000, 0.15000, 0.15000, 0.15000},
{1.00000, 0.00000, 1.00000, 0.00000, 0.00000, 0.15000, 0.15000, -0.15000},
{1.00000, 1.00000, 1.00000, 0.00000, 0.00000, 0.15000, -0.15000, -0.15000},
{0.00000, 1.00000, 0.00000, 1.00000, 0.00000, -0.15000, 0.15000, 0.15000},
{0.00000, 0.00000, 0.00000, 1.00000, 0.00000, -0.15000, 0.15000, -0.15000},
{1.00000, 0.00000, 0.00000, 1.00000, 0.00000, 0.15000, 0.15000, -0.15000},
{1.00000, 1.00000, 0.00000, 1.00000, 0.00000, 0.15000, 0.15000, 0.15000},
{0.00000, 1.00000, 0.00000, -1.00000, 0.00000, -0.15000, -0.15000, -0.15000},
{0.00000, 0.00000, 0.00000, -1.00000, 0.00000, -0.15000, -0.15000, 0.15000},
{1.00000, 0.00000, 0.00000, -1.00000, 0.00000, 0.15000, -0.15000, 0.15000},
{1.00000, 1.00000, 0.00000, -1.00000, 0.00000, 0.15000, -0.15000, -0.15000},
};

int Box_index[Box_polygoncount][3]={
{0, 1, 2},
{2, 3, 0},
{4, 5, 6},
{6, 7, 4},
{8, 9, 10},
{10, 11, 8},
{12, 13, 14},
{14, 15, 12},
{16, 17, 18},
{18, 19, 16},
{20, 21, 22},
{22, 23, 20},
};

我将其转换为与OBJ文件中的示例头文件相同的格式，因此它看起来像：

// sphere_3d.h Header File created from Cheetah 3d sphere File

unsigned int sphereNumVerts = 24;

float sphereTexCoords [] = {
0.00000, 1.00000,
0.00000, 0.00000,
1.00000, 0.00000,
1.00000, 1.00000,
0.00000, 1.00000,
0.00000, 0.00000,
1.00000, 0.00000,
1.00000, 1.00000,
0.00000, 1.00000,
0.00000, 0.00000,
1.00000, 0.00000,
1.00000, 1.00000,
0.00000, 1.00000,
0.00000, 0.00000,
1.00000, 0.00000,
1.00000, 1.00000,
0.00000, 1.00000,
0.00000, 0.00000,
1.00000, 0.00000,
1.00000, 1.00000,
0.00000, 1.00000,
0.00000, 0.00000,
1.00000, 0.00000,
1.00000, 1.00000,
};

float sphereNormals [] = {
0.00000, 0.00000, 1.00000,
0.00000, 0.00000, 1.00000,
0.00000, 0.00000, 1.00000,
0.00000, 0.00000, 1.00000,
0.00000, 0.00000, -1.00000,
0.00000, 0.00000, -1.00000,
0.00000, 0.00000, -1.00000,
0.00000, 0.00000, -1.00000,
-1.00000, 0.00000, 0.00000,
-1.00000, 0.00000, 0.00000,
-1.00000, 0.00000, 0.00000,
-1.00000, 0.00000, 0.00000,
1.00000, 0.00000, 0.00000,
1.00000, 0.00000, 0.00000,
1.00000, 0.00000, 0.00000,
1.00000, 0.00000, 0.00000,
0.00000, 1.00000, 0.00000,
0.00000, 1.00000, 0.00000,
0.00000, 1.00000, 0.00000,
0.00000, 1.00000, 0.00000,
0.00000, -1.00000, 0.00000,
0.00000, -1.00000, 0.00000,
0.00000, -1.00000, 0.00000,
0.00000, -1.00000, 0.00000,
};

float sphereVerts [] = {
-0.15000, -0.15000, 0.15000,
-0.15000, 0.15000, 0.15000,
0.15000, 0.15000, 0.15000,
0.15000, -0.15000, 0.15000,
0.15000, -0.15000, -0.15000,
0.15000, 0.15000, -0.15000,
-0.15000, 0.15000, -0.15000,
-0.15000, -0.15000, -0.15000,
-0.15000, -0.15000, -0.15000,
-0.15000, 0.15000, -0.15000,
-0.15000, 0.15000, 0.15000,
-0.15000, -0.15000, 0.15000,
0.15000, -0.15000, 0.15000,
0.15000, 0.15000, 0.15000,
0.15000, 0.15000, -0.15000,
0.15000, -0.15000, -0.15000,
-0.15000, 0.15000, 0.15000,
-0.15000, 0.15000, -0.15000,
0.15000, 0.15000, -0.15000,
0.15000, 0.15000, 0.15000,
-0.15000, -0.15000, -0.15000,
-0.15000, -0.15000, 0.15000,
0.15000, -0.15000, 0.15000,
0.15000, -0.15000, -0.15000,
};

我想使用glDrawArrays而不是glDrawElements，这样我就不会使用索引数组。当我在我的程序中尝试子站点我的自定义对象的头文件而不是示例程序中的示例文件时，形状通常(在某种程度上)看起来像我的替换对象。许多三角形都是关闭的，并且没有连接到它们应该连接的地方。

我知道我的顶点被传递到glDrawArrays的顺序是不正确的，但我不知道为什么。如何对它们进行排序，使它们按照glDrawArrays所需的顺序排列？

不想使用glDrawElements有什么原因吗？如果你查看Cheetah3D头文件中的Box_index数组，你会发现一些顶点被多次使用，这意味着要使用glDrawArrays绘制同一个对象，你必须复制一些顶点(因此需要更多的内存)。使用Box_index数组，您可以使用glDrawElements:绘制对象

glDrawElements(GL_TRIANGLES, Box_polygoncount * 3, GL_UNSIGNED_INT, Box_index);

(请注意，如果您有0-256个顶点，则应使用字节作为索引，如果您的顶点数在257-65536之间，则使用空头)

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