Geometry Clipmaps Terrain Tutorial with Source

Sven · 2014-03-18T21:36:21

After browsing the web for a usable terrain lib, I ended up writing one myself as the others were simply too bloated. I am sharing the result now as a tutorial and hope it will help the one or other of you to get started with terrain rendering. The main code as only 200 lines, so is easy to understand. Performance is around 1000 fps. Key settings:Space : wireframe viewEnter : Top-down view You can fetch the zip with all required includes from here or from the attachment. Changelog: Bugfix applied: glDrawArrays( GL_LINES, 0, vert.size()); (old) -> glDrawArrays( GL_LINES, 0, vert.size()/3); (new / ok) /////////////////////////////////////////// int grid= 64; // patch resolution int levels=5; // LOD levels int width=2048,height=2048; // heightmap dimensions /////////////////////////////////////////// void DrawScene() { if ( GetAsyncKeyState(VK_ESCAPE) ) exit(0); POINT cursor; GetCursorPos(&cursor); // mouse pointer position bool wireframe= GetAsyncKeyState(VK_SPACE); // render wireframe bool topdown = GetAsyncKeyState(VK_RETURN); // view top-down float viewangle= float(cursor.x)/5.0; vec3f viewpos ( (timeGetTime()>>2)&((1<<17)-1) , -(float(cursor.y)/1000.0)* 0.1-0.01 , 0 ); glClearDepth(1.0f); glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glEnable(GL_CULL_FACE); glCullFace(GL_FRONT); glEnable(GL_DEPTH_TEST); glDepthFunc(GL_LESS); static int tex_heightmap=0; static int tex_terrain=0; static bool init=true; static Shader shader("Shader"); static int vbo=0; static std::vector<float> vert; if(init) { /*+++++++++++++++++++++++++++++++++++++*/ // terrain heightmap Bmp bmp(width,height,32); loopj(0,height) loopi(0,width) { float x= float(i)/float(width); float y= float(j)/float(height); float h = (sin(4*M_PI*x)+sin(4*M_PI*y)+sin(16*M_PI*x)*sin(16*M_PI*y))*0.125+0.5; ((float*)bmp.data)[i+j*width]=h; } //bmp.load_float("../result.f32"); // <-- use this for loading raw float map from file tex_heightmap = ogl_tex_new(width,height,GL_LINEAR_MIPMAP_LINEAR,GL_REPEAT,GL_LUMINANCE16F_ARB,GL_LUMINANCE,bmp.data, GL_FLOAT); /*+++++++++++++++++++++++++++++++++++++*/ // terrain texture loopj(0,height) loopi(0,width) loopk(0,3) { bmp.data[(i+j*width)*3+k]=i^j^(k*192); } tex_terrain = ogl_tex_new(width,height,GL_LINEAR_MIPMAP_LINEAR,GL_REPEAT,GL_RGB,GL_RGB,bmp.data, GL_UNSIGNED_BYTE); /*+++++++++++++++++++++++++++++++++++++*/ // driver info std::cout << "GL_VERSION: " << glGetString(GL_VERSION) << std::endl; std::cout << "GL_RENDERER: " << glGetString(GL_RENDERER) << std::endl; std::cout << "GL_VENDOR: " << glGetString(GL_VENDOR) << std::endl; std::cout << "GLU_VERSION: " << gluGetString(GLU_VERSION) << std::endl; std::cout << "GLUT_API_VERSION: " << GLUT_API_VERSION << std::endl; /*+++++++++++++++++++++++++++++++++++++*/ // load shaders shader.attach(GL_VERTEX_SHADER,"../shader/vs.txt"); shader.attach(GL_FRAGMENT_SHADER,"../shader/frag.txt"); shader.link(); /*+++++++++++++++++++++++++++++++++++++*/ // make vbo quad patch loopj(0,grid+1) loopi(0,grid+2) { loopk(0, ((i==0) ? 2 : 1) ) { vert.push_back(float(i)/grid); vert.push_back(float(j)/grid); vert.push_back(0); } ++j; loopk(0, ((i==grid+1) ? 2 : 1) ) { vert.push_back(float(i)/grid); vert.push_back(float(j)/grid); vert.push_back(0); } --j; } /*+++++++++++++++++++++++++++++++++++++*/ glGenBuffers(1, (GLuint *)(&vbo)); glBindBuffer(GL_ARRAY_BUFFER, vbo); glBufferData(GL_ARRAY_BUFFER, sizeof(float)*vert.size(),&vert[0], GL_DYNAMIC_DRAW_ARB ); /*+++++++++++++++++++++++++++++++++++++*/ init=false; /*+++++++++++++++++++++++++++++++++++++*/ } glMatrixMode( GL_PROJECTION); glLoadIdentity(); if (topdown) { glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0); glRotatef(180,1,0,0); wireframe^=1; } else { int vp[4]; glGetIntegerv(GL_VIEWPORT, vp); gluPerspective(90.0,float(vp[2])/float(vp[3]) , 0.0001, 1.0); glTranslatef(0,viewpos.y,0); // set height glRotatef(130,1,0,0); glRotatef(viewangle,0,0,1); // set rotation } matrix44 mat; glGetFloatv(GL_PROJECTION_MATRIX, &mat.m[0][0]); // Enable VBO glBindBufferARB(GL_ARRAY_BUFFER_ARB, vbo); glEnableClientState(GL_VERTEX_ARRAY); glVertexPointer ( 3, GL_FLOAT,0, (char *) 0); glEnable(GL_TEXTURE_2D); glActiveTextureARB( GL_TEXTURE0 ); glBindTexture(GL_TEXTURE_2D, tex_heightmap); glEnable(GL_TEXTURE_2D); glActiveTextureARB( GL_TEXTURE1 ); glBindTexture(GL_TEXTURE_2D, tex_terrain); // Triangle Mesh shader.begin(); shader.setUniform1i("tex_heightmap",0); shader.setUniform1i("tex_terrain",1); float sxy=2; // scale x/y shader.setUniform4f("map_position", -viewpos.x/float(2*512*grid), -viewpos.z/float(2*512*grid),0,0); loopi(0,levels) { float ox=(int(viewpos.x*(1<<i))&511)/float(512*grid); float oy=(int(viewpos.z*(1<<i))&511)/float(512*grid); vec3f scale (sxy*0.25,sxy*0.25,1); shader.setUniform4f("scale" , scale.x,scale.y,1,1); loopk(-2,2) loopj(-2,2) // each level has 4x4 patches { if(i!=levels-1) if(k==-1||k==0) if(j==-1||j==0) continue; vec3f offset(ox+float(j),oy+float(k),0); if(k>=0) offset.y-=1.0/float(grid); // adjust offset for proper overlapping if(j>=0) offset.x-=1.0/float(grid); // adjust offset for proper overlapping //cull int xp=0,xm=0,yp=0,ym=0,zp=0; looplmn(0,0,0,2,2,2) { vec3f v = scale*(offset+vec3f(l,m,float(-n)*0.05)); // bbox vector vec4f cs = mat * vec4f(v.x,v.y,v.z,1); // clipspace if(cs.z< cs.w) zp++; if(cs.x<-cs.w) xm++; if(cs.x>cs.w) xp++; if(cs.y<-cs.w) ym++; if(cs.y>cs.w) yp++; } if(zp==0 || xm==8 || xp==8 || ym==8 || yp==8)continue; // skip if invisible //render shader.setUniform4f("offset", offset.x,offset.y,0,0); if(wireframe) glDrawArrays( GL_LINES, 0, vert.size()/3); else glDrawArrays( GL_TRIANGLE_STRIP, 0, vert.size()/3); } sxy*=0.5; } shader.end(); // Disable VBO glDisableClientState(GL_VERTEX_ARRAY); glBindBufferARB(GL_ARRAY_BUFFER_ARB, 0); glutSwapBuffers(); } /////////////////////////////////////////// int main(int argc, char **argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH); glutInitWindowSize(1024, 512); glutInitWindowPosition(0, 0); glutCreateWindow("Geometry Clipmaps Example"); glutDisplayFunc(DrawScene); glutIdleFunc(DrawScene); glewInit(); wglSwapIntervalEXT(0); glutMainLoop(); return 0; } ///////////////////////////////////////////

Graphics and GPU Programming Programming

Started by spacerat January 29, 2014 10:00 AM

12 comments, last by L. Spiro 10 years, 1 month ago

dpadam450

2,403

March 16, 2014 02:37 AM

You can leave it as drawing triangle strips, but set glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); to get wire-frame triangles.

I do that with my terrain and it kills the performance. I haven't thought about why as there isn't much overwrie on my terrain (about 0 triangles mapping ot the same pixel to make overdraw). I assume that the polygonMode stll runs the pixel shader on all triangles pixels and not just the edges, but then later discards writing in depth/color for the non edge pixels. Only explanation I can think of off the top of my head. Goes from like 150FPS to 20 or something. so the inner triangle pixels would be overwritten a TON of times in my case.

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spacerat

1,187

Author

March 18, 2014 07:38 AM

I just tried to implement GL_FRONT_AND_BACK in the terrain tutorial - however it doesnt give the desired result. The problem is that I used degenerated triangles at the boundaries of the quad mesh - therefore there are lots of "error-lines" on the screen. To solve this, one would have to create an alternative quad mesh that is not using degenerated triangles.