什么是正确的观点矩阵的HUD相机？ [英] What is The Correct View Matrix For The HUD Camera?

问题描述

我使用OpenSceneGraph的Andr​​oid中使用GLES2。

I'm using OpenSceneGraph in Android with GLES2.

我有两个摄像头：一个用于现场和其他的HUD。现场摄像头在我的osgViewer主摄像头。我的问题是与HUD的摄像头。我想一个OSG的几何形状添加到2D场景（HUD摄像头），但似乎无法得到它展现出来。

I have two cameras: one for the scene and the other for the HUD. The scene camera is the main camera in my osgViewer. My trouble is with the HUD's camera. I am trying to add an OSG geometry to the 2D scene (HUD camera) but can't seem to get it to show up.

我使用自定义着色器来操作几何图形的位置。据我了解的投影矩阵是正确的，但我认为问题可能与视图矩阵，因为我使用两台摄像机。我试过设置HUD的观点是现场的初步意见，但无济于事。如果我错了这个请大家指正。

I'm using custom shaders to manipulate the geometry's position. To my understanding the projection matrix is correct but I think the problem may be with the view matrix since I'm using two cameras. I've tried setting the HUD's view to be the scene's initial view but to no avail. Please correct me if I am wrong in this.

   // New camera for the HUD
   hud_camera = new osg::Camera;

   // Set the camera's view properties
   hud_camera->setProjectionMatrix(
      osg::Matrix::ortho2D(0, 1280, 0, 696));
   hud_camera->setReferenceFrame(osg::Transform::ABSOLUTE_RF);
   hud_camera->setViewMatrix(osg::Matrix::identity());
   hud_camera->setViewport(0, 0, 1280, 696);

   // Clear the depth buffer
   hud_camera->setClearMask(GL_DEPTH_BUFFER_BIT);

   // Draw the subgraph after the main camera view and don't allow this camera
   // to grab evente focurs from the main camera
   hud_camera->setRenderOrder(osg::Camera::POST_RENDER);
   hud_camera->setAllowEventFocus(false);


   osg::Geode *       geode;
   osg::Geometry *    geom;
   osg::Vec3Array *   vertices;
   osg::Program *     program;

   // Create the geode and geometry to hold the crosshair image
   geode = new osg::Geode;
   geom = new osg::Geometry;
   geode->addDrawable(geom);
   hud_camera->addChild(geode);

   // Set the vertices
   vertices = new osg::Vec3Array;
   vertices->push_back(osg::Vec3(0.0, 0.0, 0.0));
   vertices->push_back(osg::Vec3(1.0, 0.0, 0.0));
   vertices->push_back(osg::Vec3(1.0, 0.0, 1.0));
   vertices->push_back(osg::Vec3(0.0, 0.0, 1.0));
   geom->setVertexArray(vertices);

   // set colors
   osg::Vec4Array* colors = new osg::Vec4Array;
   colors->push_back(osg::Vec4(1.0, 0.0, 0.0, 1.0));
   colors->push_back(osg::Vec4(0.0, 1.0, 0.0, 1.0));
   colors->push_back(osg::Vec4(0.0, 0.0, 1.0, 1.0));
   colors->push_back(osg::Vec4(1.0, 0.0, 1.0, 1.0));
   geom->setVertexAttribArray(7, colors);
   geom->setVertexAttribBinding(7, osg::Geometry::BIND_PER_VERTEX);

   // Set primitive set
   geom->addPrimitiveSet(new osg::DrawArrays(GL_QUADS, 0, 4));
   geom->setUseVertexBufferObjects(true);

   // Vertex Shader
   char vertSource[] =
   "attribute vec4 osg_Vertex;\n"
   "attribute vec4 a_col;"
   "uniform mat4 osg_ModelViewProjectionMatrix;\n"
   "uniform mat4 proj_matrix;\n"
   "uniform mat4 view_matrix;\n"
   "varying vec4 v_col;"
   "void main(void)\n"
   "{\n"
   "gl_Position = view_matrix * proj_matrix * osg_Vertex;\n"
   "v_col = a_col;\n"
   "}\n";

   // Fragment shader
   char fragSource[] =
   "precision mediump float;\n"
   "varying vec4 v_col;"
   "void main(void)\n"
   "{\n"
   "gl_FragColor = v_col;\n"
   "}\n";

   // Set the shaders
   program = new osg::Program;
   program->setName("Crosshair Shader");
   program->addShader(new osg::Shader(osg::Shader::VERTEX, vertSource));
   program->addShader(new osg::Shader(osg::Shader::FRAGMENT, fragSource));
   program->addBindAttribLocation("a_col", 7);

   osg::StateSet* state = geode->getOrCreateStateSet();
   state->addUniform(
      new osg::Uniform("proj_matrix", hud_camera->getProjectionMatrix()));
   state->addUniform(
      new osg::Uniform("view_matrix", hud_camera->getViewMatrix());

   // Add the program shaders
   geode->getOrCreateStateSet()->setAttributeAndModes(
      program, osg::StateAttribute::ON );

   // Needs no lighting or any depth for a 2D image
   geode->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
   state->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF);

后来我附上的 hud_camera 作为一个孩子的场景数据。也在现场摄像机无为特种以外寻找在场景中的特定点。

Afterwards I attach the hud_camera as a child to the scene data. Also the scene camera is doing nothing special other than looking at a particular point in the scene.

我不知道正在创建几何事实。通过在顶点着色器使用这样的：

I do know for a fact that the geometry is being created. By using this in the vertex shader:

GL_POSITION = osg_ModelViewProjectionMatrx * osg_Vertex

我可以看到它关到场景左侧。

I can see it off to the left in the scene.

推荐答案

首先，你不应该执行视图* * PROJ顶点，它应该是凸出*查看*顶点。

First of all, you shouldn't be performing view * proj * vertex, it should be proj * view * vertex.

对于HUD，我认为并不真的需要有一个视图矩阵的。我的理解是，你只是想在屏幕上画一个平面四？

For a hud I think don't really need to have a view matrix at all. My understanding is that you just want to draw a flat quad on the screen?

如果您的投影矩阵图（0,0）到（1280,696），那么你可以只画在这个坐标系中的对象（从（0,0四）至（640696）将覆盖的左半屏幕等）。

If your projection matrix maps (0,0) to (1280,696), then you can just draw objects in this coordinate system (a quad from (0,0) to (640,696) will cover the left half of the screen, etc).

或者，如果你想画的东西从（0,0）的空间（1,1），那么只需重写投影矩阵来映射这个空间。它没有多大意义，我为参与作为HUD一样简单视图矩阵。

Or if you want to draw things in the space from (0,0) to (1,1) then just override the projection matrix to map this space. It doesn't make much sense to me to involve a view matrix for something as simple as a HUD.

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