OpenSceneGraph 3.0 Beginners Guide. WGM # 52 Gustavo Rovelo

Transcription

1 OpenSceneGraph 3.0 Beginners Guide Chapter 6. Creating Realistic Rendering Effects WGM # 52 Gustavo Rovelo April 27th, 2012

2 2 Index OpenGL state machine in OSG Setting up different rendering attributes and modes for scene objects Inheriting rendering states in the scene graph Controlling scene lights Adding textures to geometry Drawing transparent and translucent objects Working with vertex, geometry and fragment shaders

3 3 OpenGL State Machine in OSG OpenGL state machine Configuration of the drawing system at any particular time Depth test Textures Lights Color Line width OSG encapsulates the OpenGL state machine to manage the scene graph culling and rendering traversals

4 4 OpenGL State Machine in OSG The osg::stateset class Can be applied to: Nodes or Drawableobjects node->setstateset( stateset); stateset = node->getorcreatestateset(); * It distinguish between texture and nontextures attributes and modes. setattribute(osg::stateattribute) setmode(osg::stateattribute::on/off) setattributeandmodes(osg::stateattribute, osg::stateattribute::on/off) Texture attributes and modes methods require and extra parameter to specify the texture unit, and the names have the Texture infix settextureattributeandmodes( texunit, texattribute, mode);

5 5 OpenGL State Machine in OSG Example #1 model1 = osgdb::readnodefile( "cessna.osg" ); transformation1 = new MatrixTransform(); transformation2 = new MatrixTransform(); transformation1->setmatrix( Matrix::translate( Vec3(-25.0, 0.0, 0.0) ) ); transformation1->addchild( model1.get() ); transformation2->setmatrix( Matrix::translate( Vec3( 25.0, 0.0, 0.0) ) ); transformation2->addchild( model1.get() ); //Create a rendering attribute to modify t he way the model is drawn pm = new PolygonMode(); pm->setmode( PolygonMode::FRONT_AND_BACK, PolygonMode::LINE ); //Get and attach the statesetfrom and to the node stateset = transformation1->getorcreatestateset(); stateset->setattribute( pm.get() );

6 6 Inheriting Render States The state set of a node will affect the node and it s children. A node can: Inherit, stateset->setattribute( attr, osg::stateattribute::inherit ); Override or, stateset->setattribute( attr, osg::stateattribute::override ); Protect (ignore), stateset->setattribute( attr, osg::stateattribute::protected ); Set PolygonMode to Outlined Inherit Override Outlined Inherit Set PolygonMode to Filled Protected Filled Outlined

7 7 Inheriting Render States Example #2 model1 = osgdb::readnodefile( glider.osg"); transformation1 = new MatrixTransform(); transformation2 = new MatrixTransform(); transformation1->setmatrix( Matrix::translate( Vec3(-0.5, 0.0, 0.0) )); transformation1->addchild( model1.get() ); transformation2->setmatrix( Matrix::translate( Vec3( 0.5, 0.0, 0.0) )); transformation2->addchild( model1.get() ); transformation1->getorcreatestateset()->setmode( GL_LIGHTING, StateAttribute::OFF ); transformation2->getorcreatestateset()->setmode( GL_LIGHTING, StateAttribute::OFF StateAttribute::PROTECTED ); root->getorcreatestateset()->setmode( GL_LIGHTING, StateAttribute::ON StateAttribute::OVERRIDE );

8 8 OpenGL Rendering Attributes and Modes in OSG Several classes that derives from classes that derived from StateAtribute class...\include\osg\stateattribute Type ID Class name Associatedmode Related OpenGL functions BLENDFUNC osg::blendfunc GL_BLEND glblendfunc() and glblendfunseparate() COLORMASK osg::colormask - glcolormask() DEPTH osg::depth GL_DEPTH_TEST gldepthfun(), gldepthrange(), and gldepthmask() LINEWIDTH osg::linewidth - gllinewidth() LIGHT osg::light GL_LIGHTi() i=[0,7] gllight() Used as parameter of stateset->getattribute(stateattribute::polygonmode); Null pointer if the attribute has not been set

9 9 OpenGL Rendering Attributes and Modes in OSG Several classes that derives from classes that derived from StateAtribute class...\include\osg\stateattribute Type ID Class name Associatedmode Related OpenGL functions BLENDFUNC osg::blendfunc GL_BLEND glblendfunc() and glblendfunseparate() COLORMASK osg::colormask - glcolormask() DEPTH osg::depth GL_DEPTH_TEST gldepthfun(), gldepthrange(), and gldepthmask() LINEWIDTH osg::linewidth - gllinewidth() LIGHT osg::light GL_LIGHTi() i=[0,7] gllight() The way OSG calls OpenGL modes stateset->setattributeandmodes(stateattribute::gl_lighting); stateset->getmode( GL_LIGHTING );

10 10 OpenGL Rendering Attributes and Modes in OSG Example #3 fog= new Fog(); fog->setmode( Fog::LINEAR ); fog->setstart( 500.0f ); fog->setend( f); fog->setcolor( Vec4(1.0f,1.0f,0.0f,1.0f) ); model1= osgdb::readnodefile( "lz.osg" ); model1->getorcreatestateset()->setattributeandmodes( fog.get() ); viewer.setscenedata( model1.get() );

11 11 Lights and Light Sources osg::light class 8 Light sources as OpenGL It won t automatically generate and cast shadows OSG provide different methods to handle lights properties osg::lightsource class Add lights to the scene graph It should be used as a leaf node with a single light attribute All the other nodes with GL_LIGHTimode ON will be affected by it. Can be treated as a geometry representing the physical shape of the light

12 12 Lights and Light Sources Example #4 Node* createlightsource( unsigned int num, const Vec3 trans, const Vec4 color){ ref_ptr<light> light; ref_ptr<lightsource> lightsource; ref_ptr<matrixtransform> sourcetrans; light = new Light(); light->setlightnum( num); light->setdiffuse( color ); light->setposition( Vec4(0.0f,0.0f,0.0f,1.0) ); lightsource = new LightSource(); lightsource->setlight( light ); sourcetrans = new MatrixTransform(); sourcetrans->setmatrix( Matrix::translate( trans) ); sourcetrans->addchild( lightsource.get() ); return sourcetrans.release(); } int main (int argc, char** argv){ light0 = createlightsource( 0, Vec3(-20.0f, 0.0f, 0.0f), Vec4(1.0f,1.0f,0.0f,1.0f) ); light1 = createlightsource( 1, Vec3( 0.0f,-20.0f, 0.0f), Vec4(0.0f,1.0f,1.0f,1.0f) ); root->getorcreatestateset()->setmode( GL_LIGHT0, StateAttribute::ON ); root->getorcreatestateset()->setmode( GL_LIGHT1, StateAttribute::ON ); root->addchild( light0 ); root->addchild( light1 ); }

13 13 The Image Class The osg::image class manage everything related to images. To load an image from disk use: ref_ptr<osg::image> img = osgdb::readimagefile( picture.bmp ) BMP, JPG, PNG, TIFF, etc. getpixelformat() -> GL_RGB t getdatatype()->gl_unsigned_byte s getdata() unsigned char*

14 14 Texture Mapping osg::texture class encapsulates all kinds of textures. To use texture mapping in OSG we have to: Set texture coordinates to the geometry. Normalized [0,1] Set the texture mapping unit (0 to use only one) Load the image(s) we will use as texture(s) Set the texture attribute and modes to a state set Set the state set to the geometry

15 15 Texture Mapping Example #5 quad = new Geometry(); quad->setvertexarray( vertices.get() ); quad->setnormalarray( normals.get() ); quad->setnormalbinding(geometry::bind_overall); quad->settexcoordarray( 0, texcoords.get() ); quad->addprimitiveset( new DrawArrays(GL_QUADS, 0, 4) ); texture = new Texture2D(); image = osgdb::readimagefile( "Images/lz.rgb" ); texture->setimage( image.get() ); root = new Geode(); root->adddrawable( quad.get() ); root->getorcreatestateset()->settextureattributeandmodes( 0, texture.get() );

16 16 Handling Rendering Order It s especially important when using blending options to render transparent objects. Opaque objects first Translucent objects second Opaque objects second Translucent objects fisrt setrenderinghint() method of the osg::stateset class control the rendering order or nodes and drawables, drawing opaque objects first. node->getorcreatestateset()->setrenderinghint(osg::stateset::transparent_bin);

17 17 Handling Rendering Order Example # 6 texture = new Texture2D(); image = osgdb::readimagefile( "Images/lz.rgb" ); texture->setimage( image.get() ); blendfunc = new BlendFunc(); blendfunc->setfunction( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA ); stateset =geode->getorcreatestateset(); stateset->settextureattributeandmodes( 0, texture.get() ); stateset->setattributeandmodes( blendfunc.get() ); stateset->setrenderinghint(stateset::transparent_bin ); root = new Group(); root->addchild( geode.get() ); root->addchild( osgdb::readnodefile( "glider.osg" ) );

18 18 Understanding Graphic Shaders OpenGL Shading Language (GLSL) allow Programmability in the rendering pipeline at the vertex and fragment level Get more realistic rendering effects, instead of using only the fixed-function states. Shadersare written in a text file like C programs. Shaderstotally replace fixed functionalities (fog, lighting, texture mapping, etc.)

19 19 Understanding Graphic Shaders You can specify only one shaderper type: Vertex Transformations to each vertex Geometry Regenerate geometry from existing vertices Fragment Color of individual pixels

20 20 Understanding Graphic Shaders OSG defines osg::shader class setshadersource(string) setshadersourcefromfile() osgdbdefines one method to read shadersources and check shadertypes according to file extensions osg::shader* frshader=osgdb::readshaderfile( source.frag ); After we load the shadersource we have to use the osg::program class to add the shadersto a state set.

21 21 Understanding Graphic Shaders There are three types of inputs and outputs in a tyipical shader: Uniforms Read-Only during shaderexecution. Vertex attributes Writable by host applications Varyings Passing data from shaderto another. Invisible to external programs osg::uniform defines a GLSL uniform variable float leght = 1.0f; osg::ref_ptr<osg::uniform> = new osg::uniform( length, length );

22 22 Understanding Graphic Shaders There should be a variable defined in one of the loaded shader sources uniform float length; Otherwise, the uniform variable will not be available. Uniforms can be of any basic type or any aggregation of types: Boolean Float Integer 2D/3D/4D vector Matrix Texture samplers

23 23 Understanding Graphic Shaders Example #7 static const char* vertsource = { "varying vec3 normal;\n "void main()\n "{\n normal = normalize(gl_normalmatrix * gl_normal);\n" gl_position = ftransform();\n "}\n" }; static const char* fragsource = { uniform vec4 color1;\n uniform vec4 color2;\n uniform vec4 color3;\n uniform vec4 color4;\n varying vec3 normal;\n void main()\n {\n float intensity = dot(vec3(gl_lightsource[0].position), normal);\n if( intensity > 0.95) gl_fragcolor = color1;\n else if(intensity > 0.5) gl_fragcolor = color2;\n else if(intensity > 0.25) gl_fragcolor = color3;\n else gl_fragcolor = color4;\n }\n" };

24 24 Understanding Graphic Shaders Example 6-8 static const char* geomsource = { "#version 120\n "#extension GL_EXT_geometry_shader4 : enable\n "uniform int segments;\n "void main()\n "{\n " float delta = 1.0 / float(segments);\n " vec4 v;\n " for( int i=0; i <= segments; i++ )\n " {\n " float t = delta * float(i);\n " float t2 = t * t;\n " float one_minus_t = t;\n«" float one_minus_t2 = one_minus_t * one_minus_t;\n " v = gl_positionin[0] * one_minus_t2 * one_minus_t +\n " gl_positionin[1] * 3.0 * t * one_minus_t2 +\n«" gl_positionin[2] * 3.0 * t2 * one_minus_t +\n«" gl_positionin[3] * t2 * t;\n " gl_position = v;\n " EmitVertex();\n " }\n " EndPrimitive();\n "}\n" };

25 25 References RiuWang and XueleiQian. OpenSceneGraph 3.0 Beginner s guide Chapter 6 Creating Realistic Rendering Effects Pages: Ed. Packt Publishing 2010