CloudCompare源码_显示渲染的程序架构

这一讲介绍一下CloudCompare的大致绘制流程或者说绘图框架的结构。

根据前面一篇对CloudCompare读取PLY文件的介绍 ，很容易找出当cloudcompare读取到mesh文件（newGroup）后，会把这个文件通过addDB加载到根对象下面，

1.  
   //ref. mainwindow.cpp
2.  
   void MainWindow::addToDB( const QStringList& filenames,
3.  
   QString fileFilter/*=QString()*/,
4.  
   ccGLWindow* destWin/*=nullptr*/)
5.  
   {
6.  
   addToDB(newGroup, true, true, false);
7.  
   ....
8.  
   }
9.  
    
10.  
     
11.  
     
12.  
    void MainWindow::addToDB( ccHObject* obj,
13.  
    bool updateZoom/*=true*/,
14.  
    bool autoExpandDBTree/*=true*/,
15.  
    bool checkDimensions/*=true*/,
16.  
    bool autoRedraw/*=true*/)
17.  
    {
18.  
    ......
19.  
    //add object to DB root
20.  
    if (m_ccRoot)
21.  
    {
22.  
    //force a 'global zoom' if the DB was emtpy!
23.  
    if (!m_ccRoot->getRootEntity() || m_ccRoot->getRootEntity()->getChildrenNumber() == 0)
24.  
    {
25.  
    updateZoom = true;
26.  
    }
27.  
    m_ccRoot->addElement(obj, autoExpandDBTree);
28.  
    }
29.  
    ......
30.  
    }

这个根对象，就是ccDBRoot，

1.  
   //ref. ccDBRoot.h
2.  
   //! GUI database tree root
3.  
   class ccDBRoot : public QAbstractItemModel
4.  
   {
5.  
   Q_OBJECT
6.  
    
7.  
   //! Associated DB root
8.  
   ccHObject* m_treeRoot;
9.  
    
10.  
    //! Associated widget for DB tree
11.  
    QTreeView* m_dbTreeWidget;
12.  
     
13.  
    //! Associated widget for selected entity's properties tree
14.  
    QTreeView* m_propertiesTreeWidget;
15.  
     
16.  
    //! Selected entity's properties data model
17.  
    QStandardItemModel* m_propertiesModel;
18.  
    //! Selected entity's properties delegate
19.  
    ccPropertiesTreeDelegate* m_ccPropDelegate;
20.  
    ......
21.  
    }

其内部定义了一个ccHObject的指针，m_treeRoot，最终用来容纳子对像

1.  
   void ccDBRoot::addElement(ccHObject* object, bool autoExpand/*=true*/)
2.  
   {
3.  
   ......
4.  
   //look for object's parent
5.  
   ccHObject* parentObject = object->getParent();
6.  
   if (!parentObject)
7.  
   {
8.  
   //if the object has no parent, it will be inserted at tree root
9.  
   parentObject = m_treeRoot;
10.  
    m_treeRoot->addChild(object);
11.  
    }
12.  
     
13.  
    ......
14.  
    }

当然，这些都不是重点。重点是：CloudCompare是如何完成3D渲染的，相关的OpenGL函数，或者是Qt的OpenGL相关函数又封装在哪里？

下面我们慢慢来看。

相关的OpenGL函数在哪里？

OpenGL扩展函数

首先我们来看OpenGLExtensions，这些函数也就是OpenGL的扩展函数。

比如我的目录是这样的，

C:\Qt\qt5\5.15.0\msvc2019_64\include\QtOpenGLExtensions\qopenglextensions.h

在这个头文件中，不同的类封装了大量的OpenGL函数，例如，

1.  
   class QOpenGLExtension_ARB_framebuffer_object : public QAbstractOpenGLExtension
2.  
   {
3.  
   public:
4.  
   QOpenGLExtension_ARB_framebuffer_object();
5.  
    
6.  
   bool initializeOpenGLFunctions() final;
7.  
    
8.  
   void glFramebufferTextureLayer(GLenum target, GLenum attachment, GLuint texture, GLint level, GLint layer);
9.  
   void glRenderbufferStorageMultisample(GLenum target, GLsizei samples, GLenum internalformat, GLsizei width, GLsizei height);
10.  
    void glBlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1, GLbitfield mask, GLenum filter);
11.  
    void glGenerateMipmap(GLenum target);
12.  
    void glGetFramebufferAttachmentParameteriv(GLenum target, GLenum attachment, GLenum pname, GLint *params);
13.  
    void glFramebufferRenderbuffer(GLenum target, GLenum attachment, GLenum renderbuffertarget, GLuint renderbuffer);
14.  
    void glFramebufferTexture3D(GLenum target, GLenum attachment, GLenum textarget, GLuint texture, GLint level, GLint zoffset);
15.  
    void glFramebufferTexture2D(GLenum target, GLenum attachment, GLenum textarget, GLuint texture, GLint level);
16.  
    void glFramebufferTexture1D(GLenum target, GLenum attachment, GLenum textarget, GLuint texture, GLint level);
17.  
    GLenum glCheckFramebufferStatus(GLenum target);
18.  
    void glGenFramebuffers(GLsizei n, GLuint *framebuffers);
19.  
    void glDeleteFramebuffers(GLsizei n, const GLuint *framebuffers);
20.  
    void glBindFramebuffer(GLenum target, GLuint framebuffer);
21.  
    GLboolean glIsFramebuffer(GLuint framebuffer);
22.  
    void glGetRenderbufferParameteriv(GLenum target, GLenum pname, GLint *params);
23.  
    void glRenderbufferStorage(GLenum target, GLenum internalformat, GLsizei width, GLsizei height);
24.  
    void glGenRenderbuffers(GLsizei n, GLuint *renderbuffers);
25.  
    void glDeleteRenderbuffers(GLsizei n, const GLuint *renderbuffers);
26.  
    void glBindRenderbuffer(GLenum target, GLuint renderbuffer);
27.  
    GLboolean glIsRenderbuffer(GLuint renderbuffer);
28.  
     
29.  
    protected:
30.  
    Q_DECLARE_PRIVATE(QOpenGLExtension_ARB_framebuffer_object)
31.  
    };

又例如，

1.  
   class QOpenGLExtension_ARB_gpu_shader_fp64 : public QAbstractOpenGLExtension
2.  
   {
3.  
   public:
4.  
   QOpenGLExtension_ARB_gpu_shader_fp64();
5.  
    
6.  
   bool initializeOpenGLFunctions() final;
7.  
    
8.  
   void glGetUniformdv(GLuint program, GLint location, GLdouble *params);
9.  
   void glUniformMatrix4x3dv(GLint location, GLsizei count, GLboolean transpose, const GLdouble *value);
10.  
    void glUniformMatrix4x2dv(GLint location, GLsizei count, GLboolean transpose, const GLdouble *value);
11.  
    void glUniformMatrix3x4dv(GLint location, GLsizei count, GLboolean transpose, const GLdouble *value);
12.  
    void glUniformMatrix3x2dv(GLint location, GLsizei count, GLboolean transpose, const GLdouble *value);
13.  
    void glUniformMatrix2x4dv(GLint location, GLsizei count, GLboolean transpose, const GLdouble *value);
14.  
    void glUniformMatrix2x3dv(GLint location, GLsizei count, GLboolean transpose, const GLdouble *value);
15.  
    void glUniformMatrix4dv(GLint location, GLsizei count, GLboolean transpose, const GLdouble *value);
16.  
    void glUniformMatrix3dv(GLint location, GLsizei count, GLboolean transpose, const GLdouble *value);
17.  
    void glUniformMatrix2dv(GLint location, GLsizei count, GLboolean transpose, const GLdouble *value);
18.  
    void glUniform4dv(GLint location, GLsizei count, const GLdouble *value);
19.  
    void glUniform3dv(GLint location, GLsizei count, const GLdouble *value);
20.  
    void glUniform2dv(GLint location, GLsizei count, const GLdouble *value);
21.  
    void glUniform1dv(GLint location, GLsizei count, const GLdouble *value);
22.  
    void glUniform4d(GLint location, GLdouble x, GLdouble y, GLdouble z, GLdouble w);
23.  
    void glUniform3d(GLint location, GLdouble x, GLdouble y, GLdouble z);
24.  
    void glUniform2d(GLint location, GLdouble x, GLdouble y);
25.  
    void glUniform1d(GLint location, GLdouble x);
26.  
     
27.  
    protected:
28.  
    Q_DECLARE_PRIVATE(QOpenGLExtension_ARB_gpu_shader_fp64)
29.  
    };

这样的函数还有非常多，这里我就不一个一个地列举了。如果要详细了解的话，可以参考相关文档，例如，上面两个类的第一个函数分别可参考，

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glFramebufferTextureLayer.xhtml

和

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glGetUniform.xhtml

相关的函数在QCC_GL_LIB项目中用到，我们可以在CloudCompare的子项目中找到，目录地址是

libs\CCFbo\include

OpenGL各版本的函数

在Qt的源码中，这些函数的目录地址是，

qt5\5.15.0\msvc2019_64\include\QtGui\

例如我的本地地址，对应OpenGL4.5版本的函数地址是，

C:\Qt\qt5\5.15.0\msvc2019_64\include\QtGui\qopenglfunctions_4_5_core.h

由于这些类中包含的函数体量过大，这里我只贴了部分源码，如下，

1.  
   class Q_GUI_EXPORT QOpenGLFunctions_4_5_Core : public QAbstractOpenGLFunctions
2.  
   {
3.  
   public:
4.  
   QOpenGLFunctions_4_5_Core();
5.  
   ~QOpenGLFunctions_4_5_Core();
6.  
    
7.  
   bool initializeOpenGLFunctions() override;
8.  
    
9.  
   // OpenGL 1.0 core functions
10.  
    void glViewport(GLint x, GLint y, GLsizei width, GLsizei height);
11.  
    void glDepthRange(GLdouble nearVal, GLdouble farVal);
12.  
    GLboolean glIsEnabled(GLenum cap);
13.  
    void glGetTexLevelParameteriv(GLenum target, GLint level, GLenum pname, GLint *params);
14.  
    void glGetTexLevelParameterfv(GLenum target, GLint level, GLenum pname, GLfloat *params);
15.  
    void glGetTexParameteriv(GLenum target, GLenum pname, GLint *params);
16.  
    void glGetTexParameterfv(GLenum target, GLenum pname, GLfloat *params);
17.  
    void glGetTexImage(GLenum target, GLint level, GLenum format, GLenum type, void *pixels);
18.  
    const GLubyte * glGetString(GLenum name);
19.  
    void glGetIntegerv(GLenum pname, GLint *data);
20.  
    void glGetFloatv(GLenum pname, GLfloat *data);
21.  
    GLenum glGetError();
22.  
    void glGetDoublev(GLenum pname, GLdouble *data);
23.  
    void glGetBooleanv(GLenum pname, GLboolean *data);
24.  
    void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, void *pixels);
25.  
    void glReadBuffer(GLenum src);
26.  
    void glPixelStorei(GLenum pname, GLint param);
27.  
    void glPixelStoref(GLenum pname, GLfloat param);
28.  
    void glDepthFunc(GLenum func);
29.  
    void glStencilOp(GLenum fail, GLenum zfail, GLenum zpass);
30.  
    void glStencilFunc(GLenum func, GLint ref, GLuint mask);
31.  
    void glLogicOp(GLenum opcode);
32.  
    void glBlendFunc(GLenum sfactor, GLenum dfactor);
33.  
    void glFlush();
34.  
    void glFinish();
35.  
    void glEnable(GLenum cap);
36.  
    void glDisable(GLenum cap);
37.  
    void glDepthMask(GLboolean flag);
38.  
    void glColorMask(GLboolean red, GLboolean green, GLboolean blue, GLboolean alpha);
39.  
    void glStencilMask(GLuint mask);
40.  
    void glClearDepth(GLdouble depth);
41.  
    void glClearStencil(GLint s);
42.  
    void glClearColor(GLfloat red, GLfloat green, GLfloat blue, GLfloat alpha);
43.  
    void glClear(GLbitfield mask);
44.  
    void glDrawBuffer(GLenum buf);
45.  
    void glTexImage2D(GLenum target, GLint level, GLint internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const void *pixels);
46.  
    void glTexImage1D(GLenum target, GLint level, GLint internalformat, GLsizei width, GLint border, GLenum format, GLenum type, const void *pixels);
47.  
    void glTexParameteriv(GLenum target, GLenum pname, const GLint *params);
48.  
    void glTexParameteri(GLenum target, GLenum pname, GLint param);
49.  
    void glTexParameterfv(GLenum target, GLenum pname, const GLfloat *params);
50.  
    void glTexParameterf(GLenum target, GLenum pname, GLfloat param);
51.  
    void glScissor(GLint x, GLint y, GLsizei width, GLsizei height);
52.  
    void glPolygonMode(GLenum face, GLenum mode);
53.  
    void glPointSize(GLfloat size);
54.  
    void glLineWidth(GLfloat width);
55.  
    void glHint(GLenum target, GLenum mode);
56.  
    void glFrontFace(GLenum mode);
57.  
    void glCullFace(GLenum mode);
58.  
    ......
59.  
    }

以

libs\qCC_glWindow\src\ccGLUtils.cpp中了函数

DisplayTexture2DPosition

为例，其中通过QOpenGLFunctions_2_1调用了OpenGLES2.1中的函数完成相关功能，

1.  
   void ccGLUtils::DisplayTexture2DPosition(GLuint texID, int x, int y, int w, int h, unsigned char alpha/*=255*/)
2.  
   {
3.  
   QOpenGLContext* context = QOpenGLContext::currentContext();
4.  
   if (!context)
5.  
   {
6.  
   assert(false);
7.  
   return;
8.  
   }
9.  
   QOpenGLFunctions_2_1* glFunc = context->versionFunctions<QOpenGLFunctions_2_1>();
10.  
    if (glFunc)
11.  
    {
12.  
    glFunc->glBindTexture(GL_TEXTURE_2D, texID);
13.  
     
14.  
    glFunc->glPushAttrib(GL_ENABLE_BIT);
15.  
    glFunc->glEnable(GL_TEXTURE_2D);
16.  
     
17.  
    glFunc->glColor4ub(255, 255, 255, alpha);
18.  
    glFunc->glBegin(GL_QUADS);
19.  
    glFunc->glTexCoord2f(0.0, 1.0);
20.  
    glFunc->glVertex2i(x, y h);
21.  
    glFunc->glTexCoord2f(0.0, 0.0);
22.  
    glFunc->glVertex2i(x, y);
23.  
    glFunc->glTexCoord2f(1.0, 0.0);
24.  
    glFunc->glVertex2i(x w, y);
25.  
    glFunc->glTexCoord2f(1.0, 1.0);
26.  
    glFunc->glVertex2i(x w, y h);
27.  
    glFunc->glEnd();
28.  
     
29.  
    glFunc->glPopAttrib();
30.  
     
31.  
    glFunc->glBindTexture(GL_TEXTURE_2D, 0);
32.  
    }
33.  
    }

同样，在

.\libs\qCC_glWindow\src\ccGLWindow.cpp

中，对3D的渲染使用的也是QOpenGLFunctions_2_1，源码如下，

1.  
   //Default OpenGL functions set
2.  
   using ccQOpenGLFunctions = QOpenGLFunctions_2_1;
3.  
    
4.  
   void ccGLWindow::draw3D(CC_DRAW_CONTEXT& CONTEXT, RenderingParams& renderingParams)
5.  
   {
6.  
   ccQOpenGLFunctions* glFunc = functions();
7.  
   assert(glFunc);
8.  
    
9.  
   glFunc->glPointSize(m_viewportParams.defaultPointSize);
10.  
    glFunc->glLineWidth(m_viewportParams.defaultLineWidth);
11.  
     
12.  
    glFunc->glEnable(GL_DEPTH_TEST);
13.  
    ......
14.  
     
15.  
    }

CloudCompare是如何完成3D渲染的

在cloudcompare中，有一个轻量级的项目，ccViewer，如果想了解渲染的话，单看这个就够了。

渲染的函数路线如下，

ccGLWindow:

void ccGLWindow::paintGL() -->

ccGLWindow::fullRenderingPass(CONTEXT, renderingParams); -->

ccGLWindow::draw3D(CONTEXT, renderingParams); -->

ccGLWindow::drawCross()

这里，主体的绘图函数其实就是

void ccGLWindow::draw3D(CC_DRAW_CONTEXT& context, RenderingParams& params);

在该函数中，最终会调用ccHObject::draw进行绘制，

ccHObject:

ccGLWindow::draw3D(CONTEXT, renderingParams); -->

void ccHObject::draw(CC_DRAW_CONTEXT& context)

前一讲已经介绍过，打开一个mesh的时候，最终是加入到ccHObject中的container，因为打开的mesh本身也是一个ccHObject，所以实际上就是放在其m_children中，

1.  
   //Definition
2.  
    
3.  
   class QCC_DB_LIB_API ccHObject : public ccObject, public ccDrawableObject
4.  
   {
5.  
   public: //construction
6.  
   ......
7.  
   //! Standard instances container (for children, etc.)
8.  
   using Container = std::vector<ccHObject *>;
9.  
   ......
10.  
    //! Children
11.  
    Container m_children;
12.  
    ......
13.  
    }

所以在ccHObject中，绘制函数是

1.  
   void ccHObject::draw(CC_DRAW_CONTEXT& context)
2.  
   {
3.  
   ......
4.  
   //draw entity
5.  
   if (m_visible && drawInThisContext)
6.  
   {
7.  
   if (( !m_selected || !MACRO_SkipSelected(context) ) &&
8.  
   ( m_selected || !MACRO_SkipUnselected(context) ))
9.  
   {
10.  
    //apply default color (in case of)
11.  
    ccGL::Color4v(glFunc, context.pointsDefaultCol.rgba);
12.  
     
13.  
    //enable clipping planes (if any)
14.  
    bool useClipPlanes = (draw3D && !m_clipPlanes.empty());
15.  
    if (useClipPlanes)
16.  
    {
17.  
    toggleClipPlanes(context, true);
18.  
    }
19.  
     
20.  
    drawMeOnly(context);
21.  
     
22.  
    //disable clipping planes (if any)
23.  
    if (useClipPlanes)
24.  
    {
25.  
    toggleClipPlanes(context, false);
26.  
    }
27.  
    }
28.  
    }
29.  
    ......
30.  
    //draw entity's children
31.  
    for (auto child : m_children)
32.  
    {
33.  
    child->draw(context);
34.  
    }
35.  
    ......
36.  
    }

这是一个递归调用函数，当要对mesh进行绘制的时候，会调用下面的这个drawMeOnly函数，这也就是Mesh的最终绘制函数，顶点和面的计算都在这里进行。

void ccMesh::drawMeOnly(CC_DRAW_CONTEXT& context)

该函数因为内容比较多，这里就不展开了，有兴趣的读者不妨自己打开看看源码。

好了，到现在为止，我们对CloudCompare的大致绘制流程或者说框架已经有了 一个初略的了解，后面有机会我们进一步深入。

本文结束。

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