我想围绕球体包裹1024 * 512图像。
这是我的代码:(并非全部显示）
在main.cpp中：
struct Vertex {
GLdouble position[3];
GLfloat color[3];
GLfloat textureUV[2];
};
void SetupGemetry() {
//Allocate 4 VBOs
glGenBuffers(4, vbo);
}
//Setting the current Buffer.
void setBuffer(int buffer_no, int no_vertices, Vertex *vertices_array)
{
glBindBuffer(GL_ARRAY_BUFFER, vbo[buffer_no]);
glBufferData ( GL_ARRAY_BUFFER, no_vertices * sizeof ( struct Vertex ), vertices_array, GL_STATIC_DRAW );
glEnableVertexAttribArray( 0 );
glVertexAttribPointer ( ( GLuint ) 0, 3, GL_DOUBLE, GL_FALSE, sizeof ( struct Vertex ), ( const GLvoid* )
offsetof(struct Vertex ,position) );
glEnableVertexAttribArray ( 1 );
glVertexAttribPointer ( ( GLuint ) 1, 3, GL_FLOAT, GL_FALSE, sizeof ( struct Vertex ), ( const GLvoid* )
offsetof(struct Vertex,color) );
//Textute Handling
glEnableVertexAttribArray( 2 );
glVertexAttribPointer(( GLuint ) 2,3,GL_FLOAT,GL_FALSE,sizeof(struct Vertex),(const GLvoid* )offsetof(struct Vertex ,texture));
}
现在在我的Sphere.cpp中（这里我加载* .bmp文件）
GLuint Sphere::loadBMP_custom(const char * imagepath)
{
// Data read from the header of the BMP file
unsigned char header[54]; // Each BMP file begins by a 54-bytes header
unsigned int dataPos; // Position in the file where the actual data begins
unsigned int width, height;
unsigned int imageSize; // = width*height*3
// Actual RGB data
unsigned char * data;
// Open the file
FILE * file = fopen(imagepath,"rb");
if (!file)
{
printf("Image could not be opened\n");
return 0;
}
//Checking the header file
if ( fread(header, 1, 54, file)!=54 )
{ // If not 54 bytes read : problem
printf("Not a correct BMP file\n");
return false;
}
if ( header[0]!='B' || header[1]!='M' )
{
printf("Not a correct BMP file\n");
return 0;
}
dataPos = *(int*)&(header[0x0A]);
imageSize = *(int*)&(header[0x22]);
width = *(int*)&(header[0x12]);
height = *(int*)&(header[0x16]);
// Some BMP files are misformatted, guess missing information
if (imageSize==0) imageSize=width*height*3; // 3 : one byte for each Red, Green and Blue component
if (dataPos==0) dataPos=54; // The BMP header is done that way
// Create a buffer
data = new unsigned char [imageSize];
// Read the actual data from the file into the buffer
fread(data,1,imageSize,file);
//Everything is in memory now, the file can be closed
fclose(file);
//OpenGL Part
// Create one OpenGL texture
GLuint textureID;
glGenTextures(1, &textureID);
// "Bind" the newly created texture : all future texture functions will modify this texture
glBindTexture(GL_TEXTURE_2D, textureID);
// Give the image to OpenGL
glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, data);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
}
void Sphere::SetupShaders_sphere(void){
// Read our shaders into the appropriate buffers
sphere_vertexsource = filetobuf_sphere("vertex_shader_2.vert");
sphere_fragmentsource = filetobuf_sphere("fragment_shader_2.frag");
//Assign our handles a "name" to new shader objects
sphere_vertexshader = glCreateShader(GL_VERTEX_SHADER);
sphere_fragmentshader = glCreateShader(GL_FRAGMENT_SHADER);
// Associate the source code buffers with each handle
glShaderSource(sphere_vertexshader, 1, (const GLchar**)&sphere_vertexsource, 0);
glShaderSource(sphere_fragmentshader, 1, (const GLchar**)&sphere_fragmentsource, 0);
//Setting them up by compiling, attaching and linking them!
glCompileShader(sphere_vertexshader);
glCompileShader(sphere_fragmentshader);
sphere_shaderprogram = glCreateProgram();
glAttachShader(sphere_shaderprogram, sphere_vertexshader);
glAttachShader(sphere_shaderprogram, sphere_fragmentshader);
glBindAttribLocation(sphere_shaderprogram, 0, "in_Position");
glBindAttribLocation(sphere_shaderprogram, 1, "in_Color");
glLinkProgram(sphere_shaderprogram);
glUseProgram(sphere_shaderprogram);
}
现在我的片段和顶点着色器：
顶点：
#version 330 core
// Input vertex data, different for all executions of this shader.
layout(location = 0) in vec3 in_Position;
layout(location = 1) in vec3 inColor;
layout(location = 2) in vec2 vertexUV;
// Output data ; will be interpolated for each fragment.
out vec2 UV;
// Values that stay constant for the whole mesh.
uniform mat4 MVP_matrix;
void main(){
// Output position of the vertex, in clip space : MVP * position
gl_Position = MVP_matrix * vec4(in_Position,1);
// UV of the vertex. No special space for this one.
UV = vertexUV;
}
片段：
#version 330 core
// Interpolated values from the vertex shaders
in vec2 UV;
// Ouput data
out vec3 color;
// Values that stay constant for the whole mesh.
uniform sampler2D myTextureSampler;
void main(){
// Output color = color of the texture at the specified UV
color = texture2D( myTextureSampler, UV ).rgb;
}
如何将图像文件坐标（UV）转换为3D坐标？如何将它传递给我的顶点着色器？ （我知道如何将数据传递给顶点，我基本上是指如何将2D图像文件转换为3D？）例如我发现这个很好的教程
www.opengl-tutorial.org/beginners-tutorials/tutorial-5-a-textured-cube /
那说：“好吧，我们必须在这里做同样的事情，但不是给出缓冲区（R，G，B）三元组，而是给出（U，V）对的缓冲区。 “
// Two UV coordinatesfor each vertex. They were created with Blender. You'll learn shortly how to do this yourself.
static const GLfloat g_uv_buffer_data[] = {
0.000059f, 1.0f-0.000004f,
0.000103f, 1.0f-0.336048f,
0.335973f, 1.0f-0.335903f,
1.000023f, 1.0f-0.000013f,
0.667979f, 1.0f-0.335851f,
0.999958f, 1.0f-0.336064f,
0.667979f, 1.0f-0.335851f,
0.336024f, 1.0f-0.671877f,
0.667969f, 1.0f-0.671889f,
1.000023f, 1.0f-0.000013f,
0.668104f, 1.0f-0.000013f,
0.667979f, 1.0f-0.335851f,
0.000059f, 1.0f-0.000004f,
0.335973f, 1.0f-0.335903f,
0.336098f, 1.0f-0.000071f,
0.667979f, 1.0f-0.335851f,
0.335973f, 1.0f-0.335903f,
0.336024f, 1.0f-0.671877f,
1.000004f, 1.0f-0.671847f,
0.999958f, 1.0f-0.336064f,
0.667979f, 1.0f-0.335851f,
0.668104f, 1.0f-0.000013f,
0.335973f, 1.0f-0.335903f,
0.667979f, 1.0f-0.335851f,
0.335973f, 1.0f-0.335903f,
0.668104f, 1.0f-0.000013f,
0.336098f, 1.0f-0.000071f,
0.000103f, 1.0f-0.336048f,
0.000004f, 1.0f-0.671870f,
0.336024f, 1.0f-0.671877f,
0.000103f, 1.0f-0.336048f,
0.336024f, 1.0f-0.671877f,
0.335973f, 1.0f-0.335903f,
0.667969f, 1.0f-0.671889f,
1.000004f, 1.0f-0.671847f,
0.667979f, 1.0f-0.335851f
};
我必须使用搅拌机吗？ 我找到了http://www.opengl.org/wiki/Texturing_a_Sphere#2D_Texture_Mapping_a_Sphere 但我仍然无法理解
答案 0 :(得分：1)
如何将图像文件坐标（UV）转换为3D坐标？
你没有。纹理不会使您的几何体。您还需要提供球体的坐标。不，您不必使用Blender，它只是用于导出一些顶点数据（位置，法线和纹理坐标）供以后使用。因此，除了UV缓冲区外，还应该有位置和普通缓冲区。
答案 1 :(得分：1)
问题＆＃34;如何将图像文件坐标（UV）转换为3D坐标？＆＃34;声音反转。您应该问＆＃34;如何将球体坐标（3D）转换为图像坐标（UV）？教程示例使用Blender创建静态数据的UV数据。如果要计算球体的顶点，则需要同时计算UV坐标并将它们存储在Vertex结构中。或者，如果您有一组预先计算的静态球体坐标，则需要计算一组类似的UV坐标。我们的想法是获取3D数据并将其传递给一个映射函数，该函数返回U，V坐标，纹理的像素将用于该3D点。
最简单的计算是使用极坐标（方位角，高度）并将其映射到U，V范围。如果正在计算球体3D顶点，则算法可能已经使用极坐标并调用trig函数来获得X，Y，Z。
opengl.org链接提到了＆＃39; cubemap＆＃39;是纹理球体的首选方法。 ＆＃34;为获得最佳效果，请使用立方体贴图。应用2D纹理的问题在于，当您将2D纹理包裹到球体，球体的顶部和底部区域时，纹理看起来会被挤压。＆＃34;
您提出的2D地图在缠绕球体或其他3D曲线时始终会出现扭曲。可以调整U，V映射算法以最小化效果或隐藏主视线外部的接缝，但是球体旋转它们将出现在某处。