Meshes Dr. Scott Schaefer

3D Surfaces

Vertex Table

3D Surfaces Vertex Table Polygon Table

3D Surfaces Vertex Table Polygon Table

3D File Formats Way too many! OBJ STL MA PLY MAX, 3DS BLEND DAW LWO X ….

OBJ File Format (Simplified) Text Format – Easy to read! Line based file consisting of Vertices (starts with “v”) Faces (starts with “f”) Comments (starts with “#”)

OBJ File Format (Simplified) Vertex Definition “v x y z”: vertex with coordinates (x,y,z) “vt u v”: texture coordinates (u,v) “vn nx ny nz”: normal (nx,ny,nz)

OBJ File Format (Simplified) Face Definition “f g1/t1/n1 g2/t2/n2 …” Faces may be variable length! Indexing starts at 1… not 0! First index is guarantee to be geometry index ti, ni are optional

OBJ File Format – Example # This is a comment v v v v f f f f 2 3 4

OBJ File Format – Example # This is a comment v v v v vn vn vn vn f 1//2 2//1 3//3 f 1//2 3//3 4//4 f 1//2 4//4 2//1 f 2//1 3//3 4//4

OBJ File Format – Complications Vertices may appear after faces Faces may not be triangles (must triangulate) Faces may use negative indexing

3D File Formats Vertices may appear after faces Faces may not be triangles (must triangulate) Faces may use negative indexing Not all OBJ files conform to the OBJ standard

Drawing 3D Objects with OpenGL Immediate Mode Display Lists Vertex Arrays Vertex Buffer Objects

Immediate Mode glBegin ( GL_TRIANGLES ); glNormal3f ( nx1, ny1, nz1 ); glVertex3f ( x1, y1, z1 ); glNormal3f ( nx2, ny2, nz2 ); glVertex3f ( x2, y2, z2 ); … glEnd ( );

Immediate Mode Advantages Easy to send a few polygons to OpenGL Disadvantages Lots of data transferred on the stack Lots of function calls Vertices duplicated many times Really, really slow

Display Lists Initialize display list firstList = glGenLists ( numLists ); glNewList ( firstList, GL_COMPILE_AND_EXECUTE ); // draw model in immediate mode glEndList ( ); Draw the display list glCallList ( firstList );

Display Lists Relies on graphics driver for optimization Advantages Faster than immediate mode Disadvantages Still not great performance

Vertex Arrays glEnableClientState ( GL_(VERTEX/TEXTURE_COORD/NORMAL)_ARRAY ); glVertexPointer ( numComp, GL_FLOAT, bytes to next vertex, pointer to geometry) glTexCoordPointer ( numComp, GL_FLOAT, bytes to next texture coord, pointer to texture coords) glNormalPointer ( GL_FLOAT, bytes to next normal, pointer to normals ) glDrawElements ( GL_TRIANGLES, number of indices in array, GL_UNSIGNED_INT, pointer to index array) glDisableClientState ( GL_(VERTEX/TEXTURE_COORD/NORMAL)_ARRAY )

Vertex Arrays Advantages Only transfers vertices once and not an expected value of 6 times Much faster than even display lists Format similar to most mesh formats Disadvantages Still transfers vertices to GPU every frame Bandwidth to GPU very problematic

Vertex Buffer Objects New Functions glGenBuffersARB glBindBufferARB glBufferDataARB Use glVertexPointer… with NULL pointer as argument Use glDrawElements with NULL pointer as argument

Vertex Buffer Objects Advantages Can store data directly in video memory or AGP Greatly reduces bandwidth problem to GPU Disadvantages Not supported by MS OpenGL headers Must load function pointers out of DLL using WGLGetProcAddress Dynamic geometry does get as much benefit

Performance Nvidia 7300 GTNvidia 8800 GTX Immediate Mode15.5 Display Lists Vertex Arrays Vertex Buffer Objects Frames per second displaying a 413,236 triangle model. CPU was an Intel Core