Encyclopedia of Graphics File Formats Companion

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Text File | 1994-06-17 | 22.6 KB | 543 lines

ED. NOTE: This is not a formal specification, but an informal description of the format. FORM TDDD --------- FORM TDDD is used by Impulse's Turbo Silver 3.0 for 3D rendering data. TDDD stands for "3D data description". The files contain object and (optionally) observer data. Currently, in "standard IFF" terms, a FORM TDDD has only two chunk types: an INFO chunk describing observer data; and an OBJ chunk describing an object heirarchy. The INFO chunk appears in "cell" files, and the OBJ chunk appears in "cell" files and "object" files. The FORM has an (optional) INFO chunk followed by some number of OBJ chunks. (Note: OBJ is followed by a space -- ckID = "OBJ ") The INFO and OBJ chunks, in turn, are made up of smaller chunks with the standard IFF structure: <ID> <data-size> <data>. The INFO "sub-chunks" are relatively straightforward to interpret. The OBJ "sub-chunks" support object heirarchies, and are slightly more difficult to interpret. Currently, there are 3 types of OBJ sub-chunks: an EXTR chunk, describing an "external" object in a seperate file; a DESC chunk, describing one node of a heirarchy; and a TOBJ chunk marking the end of a heirarchy chain. For each DESC chunk, there must be a corresponding TOBJ chunk. And an EXTR chunk is equivalent to a DESC/TOBJ pair. In Turbo Silver, the structure of the object heirarchy is as follows. There is a head object, and its (sexist) brothers. Each brother may have child objects. The children may have grandchildren, and so on. The brother nodes are kept in a doubly linked list, and each node has a (possibly NULL) pointer to a doubly linked "child" list. The children point to the "grandchildren" lists, and so on. (In addition, each node has a "back" pointer to its parent). Each of the "head" brothers is written in a seperate OBJ chunk, along with all its descendants. The descendant heirarchy is supported as follows: for each node of a doubly linked list, 1) A DESC chunk is written, describing its object. 2) If it has children, steps 1) to 3) are performed for each child. 3) A TOBJ chunk is written, marking the end of the children. For "external" objects, steps 1) to 3) are not performed, but an EXTR chunk is written instead. (This means that an external object cannot have children unless they are stored in the same "external" file). The TOBJ sub-chunks have zero size -- and no data. The DESC and EXTR sub-chunks are made up of "sub-sub-chunks", again, with the standard IFF structure: <ID> <data-size> <data>. Reader software WILL FOLLOW the standard IFF procedure of skipping over any un-recognized chunks -- and "sub-chunks" or "sub-sub-chunks". The <data-size> field indicates how many bytes to skip. In addition it WILL OBSERVE the IFF rule that an odd <data-size> may appear, in which case the corredponding <data> field will be padded at the end with one extra byte to give it an even size. Now, on with the details. First, there are several numerical fields appearing in the data, describing object positions, rotation angles, scaling factors, etc. They are stored as "32-bit fractional" numbers, such that the true number is the 32-bit number divided by 65536. So as an example, the number 3.14159 is stored as (hexadecimal) $0003243F. This allows the data to be independant of any particular floating point format. And it (actually) is the internal format used in the "integer" version of Turbo Silver. Numbers stored in this format are called as "FRACT"s below. Second, there are several color (or RGB) fields in the data. They are always stored as three UBYTEs representing the red, green and blue components of the color. Red is always first, followed by green, and then blue. For some of the data chunks, Turbo Silver reads the color field into the 24 LSB's of a LONGword. In such cases, the 3 RGB bytes are preceded by a zero byte in the file. The following "typedef"s are used below: typedef LONG FRACT; /* 4 bytes */ typedef UBYTE COLOR[3]; /* 3 bytes */ typedef struct vectors { FRACT X; /* 4 bytes */ FRACT Y; /* 4 bytes */ FRACT Z; /* 4 bytes */ } VECTOR; /* 12 bytes total */ typedef struct matrices { VECTOR I; /* 12 bytes */ VECTOR J; /* 12 bytes */ VECTOR K; /* 12 bytes */ } MATRIX; /* 36 bytes total */ The following structure is used in generating animated cells from a single cell. It can be attached to an object or to the camera. It is also used for Turbo Silver's "extrude along a path" feature. typedef struct story { UBYTE Path[18]; /* 18 bytes */ VECTOR Translate; /* 12 bytes */ VECTOR Rotate; /* 12 bytes */ VECTOR Scale; /* 12 bytes */ UWORD info; /* 2 bytes */ } STORY; /* 56 bytes total */ The Path[] name refers to a named object in the cell data. The path object should be a sequence of points connected with edges. The object moves from the first point of the first edge, to the last point of the last edge. The edge ordering is important. The path is interpolated so that the object always moves an equal distance in each frame of the animation. If there is no path the Path[] field should be set to zeros. The Translate vector is not currently used. The Rotate "vector" specifies rotation angles about the X, Y, and Z axes. The Scale vector specfies X,Y, and Z scale factors. The "info" word is a bunch of bit flags: ABS_TRA 0x0001 - translate in world coorinates (not used) ABS_ROT 0x0002 - rotation in world coorinates ABS_SCL 0x0004 - scaling in world coorinates LOC_TRA 0x0010 - translate in local coorinates (not used) LOC_ROT 0x0020 - rotation in local coorinates LOC_SCL 0x0040 - scaling in local coorinates X_ALIGN 0x0100 - (not used) Y_ALIGN 0x0200 - align Y axis to path's direction Z_ALIGN 0x0400 - (not used) FOLLOW_ME 0x1000 - children follow parent on path INFO sub-chunks --------------- BRSH - size 82 WORD Number; ; Brush number (between 0 and 7) CHAR Filename[80]; ; IFF ILBM filename There may be more than one of these. STNC - size 82 Same format as BRSH chunk. TXTR - size 82 Same format as BRSH chunk. The Filename field is the name of a code module that can be loaded with LoadSeg(). OBSV - size 28 VECTOR Camera; ; Camera position VECTOR Rotate; ; Camera rotation angles FRACT Focal; ; Camera focal length This tells where the camera is, how it is aimed, and its focal length. The rotation angles are in degrees, and specify rotations around the X, Y, and Z axes. The camera looks down its own Y axis, with the top of the picture in the direction of the Z axis. If the rotation angles are all zero, its axes are aligned with the world coordinate axes. The rotations are performed in the order ZXY about the camera axes. A positive angle rotates Y toward Z, Z toward X, and X toward Y for rotations about the X, Y, and Z axes respectively. To understand the focal length, imagine a 320 x 200 pixel rectangle perpendicular to, and centered on the camera's Y axis. Any objects in the infinite rectangular cone defined by the camera position and the 4 corners of the rectangle will appear in the picture. OTRK - size 18 BYTE Trackname[18]; This chunk specifies the name of an object that the camera is "tracked" to. If the name is NULL, the camera doesn't track. Otherwise, if the object is moved inside Turbo Silver, the camera will follow it. OSTR - size 56 STORY CStory; ; a STORY structure for the camera The story structure is defined above. FADE - size 12 FRACT FadeAt; ; distance to start fade FRACT FadeBy; ; distance of total fade BYTE pad; ; pad byte - must be zero COLOR FadeTo; ; RGB color to fade to SKYC - size 8 BYTE pad; ; pad byte - must be zero COLOR Horizon; ; horizon color BYTE pad; ; pad byte - must be zero COLOR Zenith; ; zenith color AMBI - size 4 BYTE pad; ; pad byte - must be zero COLOR Ambient; ; abmient light color GLB0 - size 8 BYTE Props[8]; ; an array of 8 "global properties" used ; by Turbo Silver. Props[0] - GLB_EDGING ; edge level (globals requester) Props[1] - GLB_PERTURB ; perturbance (globals requester) Props[2] - GLB_SKY_BLEND ; sky blending factor (0-255) Props[3] - GLB_LENS ; lens type (see below) Props[4] - GLB_FADE ; flag - Sharp/Fuzzy focus (globals) Props[5] - GLB_SIZE ; "apparant size" (see below) Props[6] - GLB_RESOLVE ; resolve depth (globals requester) Props[7] - GLB_EXTRA ; flag - genlock sky on/off The edging and perturbance values control the heuristics in ray tracing. The sky blending factor is zero for no blending, and 255 for full blending. The lens type is a number from 0 4, corresponding to the boxes in the "camera" requester, and correspond to 0) Manual, 1) Wide angle, 2) Normal, 3) Telephoto, and 4) Custom. It is used in setting the camera's focal length if the camera is tracked to an object. The Sharp/Fuzzy flag turns the "fade" feature on and off - non-zero means on. The "apparant size" parameter is 100 times the "custom size" parameter in the camera requester. And is used to set the focal length for a custom lens. The "resolve depth" controls the number of rays the ray tracer will shoot for a single pixel. Each reflective/refractive ray increments the depth counter, and the count is never allowed to reach the "resolve depth". If both a reflective and a refractive ray are traced, each ray gets its own version of the count - so theoretically, a resolve depth of 4 could allow much more than 4 rays to be traced. The "genlock sky" flag controls whether the sky will be colored, or set to the genlock color (color 0 - black) in the final picture. All of the INFO sub-chunks are optional, as is the INFO chunk. Default values are supplied if the chunks are not present. The defaults are: no brushes, stencils, or textures defined; no story for the camera; horizon and zenith and ambient light colors set to black; fade color set to (80,80,80); un-rotated, un-tracked camera at (-100, -100, 100); and global properties array set to [30, 0, 0, 0, 0, 100, 8, 0]. DESC sub-sub-chunks ------------------- NAME - size 18 BYTE Name[18]; ; a name for the object. Used for camera tracking, specifying story paths, etc. SHAP - size 4 WORD Shape; ; number indicating object type WORD Lamp; ; number indicating lamp type Lamp numbers are: 0 - not a lamp 1 - like sunlight 2 - like a lamp - intensity falls off with distance. Shape numbers are: 0 - Sphere 1 - Stencil 2 - Axis ; custom objects with points/triangles 3 - Facets ; illegal - for internal use only 4 - Surface 5 - Ground Spheres have thier radius set by the X size parameter. Stencils and surfaces are plane-parallelograms, with one point at the object's position vector; one side lying along the object's X axis with a length set by the X size; and another side starting from the position vector and going "Y size" units in the Y direction and "Z size" units in the X direction. A ground object is an infinte plane perpendicular to the world Z axis. Its Z coordinate sets its height, and the X and Y coordinates are only relevant to the position of the "hot point" used in selecting the object in the editor. Custom objects have points, edges and triangles associated with them. The size fields are relevant only for drawing the object axes in the editor. Shape number 3 is used internally for triangles of custom objects, and should never appear in a data file. POSI - size 12 VECTOR Position; ; the object's position. Legal coordinates are in the range -32768 to 32767 and 65535/65536. Currently, the ray-tracer only sees objects in the -1024 to 1024 range. Light sources, and the camera may be placed outside that range, however. AXIS - size 36 VECTOR XAxis; VECTOR YAxis; VECTOR ZAxis; These are direction vectors for the object coordinate system. They must be "orthogonal unit vectors" - i.e. the sum of the squares of the vevtor components must equal one (or close to it), and the vectors must be perpendicular. SIZE - size 12 VECTOR Size; See SHAP chunk above. The sizes are used in a variety of ways depending on the object shape. For custom objects, they are the lengths of the coordinate axes drawn in the editor. If the object has its "Quickdraw" flag set, the axes lengths are also used to set the size of a rectangular solid that is drawn rather than drawing all the points and edges. PNTS - size 2 + 12 * point count UWORD PCount; ; point count VECTOR Points[]; ; points This chunk has all the points for custom objects. The are refered to by thier position in the array. EDGE - size 4 + 4 * edge cout UWORD ECount; ; edge count UWORD Edges[][2]; ; edges This chunk contins the edge list for custom objects. The Edges[][2] array is pairs of point numbers that are connected by the edges. Edges are refered to by thier position in the Edges[] array. FACE - size 2 + 6 * face count UWORD TCount; ; face count UWORD Connects[][3]; ; faces This chunk contains the triangle (face) list for custom objects. The Connects[][3] array is triples of edge numbers that are connected by triangles. COLR - size 4 REFL - size 4 TRAN - size 4 BYTE pad; ; pad byte - must be zero COLOR col; ; RGB color These are the main object RGB color, and reflection and transmission coefficients. CLST - size 2 + 3 * count RLST - size 2 + 3 * count TLST - size 2 + 3 * count UWORD count; ; count of colors COLOR colors[]; ; colors These are the main object color, and reflection and transmission coefficients for each face in custom objects. The count should match the face count in the FACE chunk. The ordering corresponds to the face order. TPAR - size 64 FRACT Params[16]; ; texture parameters This is the list of parameters for texture modules when texture mapping is used. SURF - size 5 BYTE SProps[5]; ; object properties This chunk contains object (surface) properties used by Turbo Silver. SProps[0] - PRP_SURFACE ; surface type ; 0 - normal ; 4 - genlock ; 5 - IFF brush SProps[1] - PRP_BRUSH ; brush number (if IFF mapped) SProps[2] - PRP_WRAP ; IFF brush wrapping type ; 0 - no wrapping ; 1 - wrap X ; 2 - wrap Z ; 3 - wrap X and Z SProps[3] - PRP_STENCIL ; stencil number for stencil objects SProps[4] - PRP_TEXTURE ; texture number if texture mapped MTTR - size 2 UBYTE Type; ; refraction type (0-4) UBYTE Index; ; custom index of refraction This chunk contains refraction data for transparent or glossy objects. If the refraction type is 4, the object has a "custom" refractive index stored in the Index field. The Index field is 100 * (true index of refraction - 1.00) -- so it must be in the range of 1.00 to 3.55. The refraction types is 0-3 specify 0) Air - 1.00, 1) Water - 1.33, 2) Glass - 1.67 or 3) Crystal 2.00. SPEC - size 2 UBYTE Specularity; ; range of 0-255 UBYTE Hardness; ; specular exponent (0-31) This chunk contains specular information. The Specularity field is the amount of specular reflection -- 0 is none, 255 is fully specular. The "specular exponent" controls the "tightness" of the specular spots. A value of zero gives broad specular spots and a value of 31 gives smaller spots. PRP0 - size 6 UBYTE Props[6]; ; more object properties This chunk contains object properties that programs other than Turbo Silver might support. Props[0] - PRP_BLEND ; blending factor (0-255) Props[1] - PRP_SMOOTH ; roughness factor Props[2] - PRP_SHADE ; shading on/off flag Props[3] - PRP_PHONG ; phong shading on/off flag Props[4] - PRP_GLOSSY ; glossy on/off flag Props[5] - PRP_QUICK ; Quickdraw on/off flag The blending factor controls the amount of dithering used on the object - 255 is fully dithered. The roughness factor controls how rough the object should appear - 0 is smooth, 255 is max roughness. The shading flag is interpreted differently depending on whether the object is a light source or not. For light sources, it sets the light to cast shadows or not. For normal objects, if the flag is set, the object is always considered as fully lit - i.e. it's color is read directly from the object (or IFF brush), and is not affected by light sources. The phong shading is on by default - a non-zero value turns it off. The glossy flag sets the object to be glossy or not. If the object is glossy, the "transmit" colors and the index of refraction control the amount of "sheen". The glossy feature is meant to simulate something like a wax coating on the object with the specified index of refraction. The trasmission coefficients control how much light from the object makes it through the wax coating. The Quickdraw flag, if set, tells the editor not to draw all the points and edges for the object, but to draw a rectanglular solid centered at the object position, and with sizes detemined by the axis lengths. INTS - size 4 FRACT Intensity; ; light intensity This is the intensity field for light source objects. an intensity of 255 for a sun-like light fully lights object surfaces which are perpendicular to the direction to the light source. For lamp-like light sources, the necessary intensity will depend on the distance to the light. STRY - size 56 STORY story; ; a story structure for the object. The story structure is described above. Again, most of these fields are optional, and defaults are supplied. However, if there is a FACE chunk, there must also be a CLST chunk, an RLST chunk and a TLST chunk -- all with matching "count" fields. The SHAP chunk is not optional. Defaults are: Colors set to (240,240,240); reflection and transmission coefficients set to zero; illegal shape; no story or special surface types; position at (0,0,0); axes aligned to the world axes; size fields all 32.0; intensity at 300; no name; no points/edges or faces; texture parameters set to zero; refraction type 0 with index 1.00; specular, hardness and roughness set to zero; blending at 255; glossy off; phong shading on; not a light source; not brightly lit; EXTR sub-sub-chunks ------------------- MTRX - size 60 VECTOR Translate; ; translation vector VECTOR Scale; ; X,Y and Z scaling factors MATRIX Rotate; ; rotation matrix The translation vector is i world coordinates. The scaling factors are with respect to local axes. The rotation matrix is with respect to the world axes, and it should be a "unit matrix". The rotation is such that a rotated axis's X,Y, and Z components are the dot products of the MATRIX's I,J, and K vectors with the un-rotated axis vector. LOAD - size 80 BYTE Filename[80]; ; the name of the external file This chunk contains the name of an external object file. The external file should be a FORM TDDD file. It may contain an any number of objects possibly grouped into heirarchy(ies). Both of these chunks are required.