osgSimplegl3结合RenderDoc工具

author: longlongwaytogo
date: 2022/07/18
email: longlongway2012@hotmail.com		
repo: https://github.com/longlongwaytogo/LearnOsgGL3

上一篇文章介绍了osg自带的osgSimple3例子，现在对它进行一定的修改，使其运行在gl 3.3 core模式下。

• 设置gl 3.3版本和启用core模式

    const std::string version( "3.3" );
    osg::ref_ptr< osg::GraphicsContext::Traits > traits = new osg::GraphicsContext::Traits();
    traits->x = 20; traits->y = 30;
    traits->width = width; traits->height = height;
    traits->windowDecoration = true;
    traits->doubleBuffer = true;
    traits->glContextVersion = version;
    traits->glContextProfileMask = GL_CONTEXT_CORE_PROFILE_BIT;// 0x1;// 

• 删除兼容代码：

        // for non GL3/GL4 and non GLES2 platforms we need enable the osg_ uniforms that the shaders will use,
        // you don't need thse two lines on GL3/GL4 and GLES2 specific builds as these will be enable by default.
        gc->getState()->setUseModelViewAndProjectionUniforms(true);
        gc->getState()->setUseVertexAttributeAliasing(true);

• 修改shader版本为将#version 330

       const std::string vertexSource =
        "#version 330 n"
        " n"
        "uniform mat4 osg_ModelViewProjectionMatrix; n"
        "uniform mat3 osg_NormalMatrix; n"
        "uniform vec3 ecLightDir; n"
        " n"
        "in vec4 osg_Vertex; n"
        "in vec3 osg_Normal; n"
        "out vec4 color; n"
        " n"
        "void main() n"
        "{ n"
        "    vec3 ecNormal = normalize( osg_NormalMatrix * osg_Normal ); n"
        "    float diffuse = max( dot( ecLightDir, ecNormal ), 0. ); n"
        "    color = vec4( vec3( diffuse ), 1. ); n"
        " n"
        "    gl_Position = osg_ModelViewProjectionMatrix * osg_Vertex; n"
        "} n";
    osg::Shader* vShader = new osg::Shader( osg::Shader::VERTEX, vertexSource );

    const std::string fragmentSource =
        "#version 330 n"
        " n"
        "in vec4 color; n"
        "out vec4 fragData; n"
        " n"
        "void main() n"
        "{ n"
        "    fragData = color; n"
        "} n";

• 设置投影矩阵和顶点属性引用，但这句代码只在gl3以前的版本中需要，真正开发gl3版本的osg程序不需要以下代码

   // for non GL3/GL4 and non GLES2 platforms we need enable the osg_ uniforms that the shaders will use,
    // you don't need thse two lines on GL3/GL4 and GLES2 specific builds as these will be enable by default.
    gc->getState()->setUseModelViewAndProjectionUniforms(true);
    gc->getState()->setUseVertexAttributeAliasing(true);

• 兼容osg原有顶点数据布局位置：

    
    // 兼容osg原有顶点数据布局位置
    gc->getState()->resetVertexAttributeAlias(false);
    

• 使用RenderDoc抓帧分析：

  • Renderdoc支持gl 3.3以后版本的OpenGL，可以实现渲染数据的记录和再现，便于分析和查错。虽然不能支持单步调试，但可以修改着色器实时看到修改后的运行结果。

  • 使用RenderDoc抓帧的界面，在程序上会显示额外的ui界面，显示Fame数目，刷新频率,抓帧快捷键F12(printscreen也可以抓帧)等信息，按下F12即可捕获一帧的渲染数据，下图为修改后的osgSimple3抓帧结果：
    

  • 点击查看捕获的数据，选择textureViewer,左侧可以看到渲染阶段的api调用，中间为当前选中缓冲区，右侧显示colorbuffer和depethbuffer资源预览图:
    

  • 点击pipeline state 可以查看不同的渲染阶段，如选中vs查看顶点shader
    

  • 顶点shader预览窗口：

  • 顶点Mesh Viewer预览窗口,可以查看渲染模型的网格信息：
    

• 总结：

  使用opengl 3.3以后的版本，结合RenderDoc等调试工具可以对开发起到事半功倍的作用，又是百思不得其解的问题，一看就知道错在哪里，感慨工具开发者必然也是被折么的无法忍受，在想着通过捕获渲染api接口和数据的思路，来分析和重现整个渲染流程。