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diff --git a/html/en/internal.html b/html/en/internal.html new file mode 100644 index 0000000..d919b84 --- /dev/null +++ b/html/en/internal.html @@ -0,0 +1,207 @@ +<html> + +<head> +<meta HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> +<title>Internal Architecture</title> +<link rel="stylesheet" type="text/css" href="../style.css"> +</head> + +<body> + +<h1>Internal Architecture</h1> + +<h3>Modularity</h3> + + + <p>Apart from the several drivers, the CD library is composed of a few modules, the public + header files <b>cd.h</b> and <b>wd.h</b>, those which implement the functions + independently from drivers,<b> cd*.c</b> and <b>wd.c</b>, and the header file <b>cd_private.h</b>, + apart from some other modules which implement non-exported specific functions. Such + modules are totally independent from the implemented drivers, as well as every driver + independs from one another, unless there is an intentional dependency.</p> + + +<h3>Linking</h3> + + + <p>Since the drivers independ from one another, we could create a library for each of + them. For the drivers provided with CD it was easy to include them in their own library, + thus simplifying the application's linking process. Note: Internally, the drivers are + called "context".</p> + <p>In order to establish this dependency, when creating a canvas in a given driver the + user must specify the driver to be used. This specification is done by means of a macro + which is actually a function with no parameter, which passes the function table from that + driver to the canvas creation function. For instance:</p> + + <pre><b>CD_PS</b> <em>(is in fact)</em> cdContextPS() +cdCreateCanvas(<b>CD_PS</b>, "teste.ps"); <em>(will do)</em> canvas-><b>Line</b> = context-><b>Line</b></pre> +<p>If the context function is not invoqued then that driver does not need to be +linked with the application. This is usefull if the application uses a custom +build of the CD library and usefull for additional drivers not included in the +main library, like IUP and PDF, that have external dependencies.</p> + + + +<h3>Structures</h3> + + + <p>The core implementation defines the structures declared in the cd.h header. + But declares an undefined structure called cdCtxCanvas. This structure is + defined in each driver according to their needs. But the first member of this + structure must be a pointer to the cdCanvas structure.</p> + <p>The drivers need not to implement all functions from the function table, + only a few are required.</p> + <p>Here is the definition of the cdContext and cdCanvas structures: </p> + <table BORDER="1" CELLPADDING="5"> + <tr> + <td><pre>struct <b>_cdContext +</b>{ + unsigned long caps; + + /* can NOT be NULL */ + void (*CreateCanvas)(cdCanvas* canvas, void *data); + void (*InitTable)(cdCanvas* canvas); + + /* can be NULL */ + int (*Play)(cdCanvas* canvas, int xmin, int xmax, int ymin, int ymax, void *data); + int (*RegisterCallback)(int cb, cdCallback func); +};</pre> + </td> + </tr> + <tr> + <td><pre>struct <b>_cdCanvas +</b>{ + ... + void (*Line)(cdCtxCanvas* ctxcanvas, int x1, int y1, int x2, int y2); + void (*Rect)(cdCtxCanvas* ctxcanvas, int xmin, int xmax, int ymin, int ymax); + void (*Box)(cdCtxCanvas* ctxcanvas, int xmin, int xmax, int ymin, int ymax); + ... + + ... + int mark_type, mark_size; + int line_style, line_width; + int interior_style, hatch_style; + ... + + cdVectorFont* vector_font; + cdSimulation* simulation; + cdCtxCanvas* ctxcanvas; // context dependent defintion + cdContext* context; +};</pre> + </td> + </tr> + </table> + + + + <p>Internally each driver defines its cdCtxCanvas strcuture:</p> +<pre>struct _cdCtxCanvas +{ + cdCanvas* canvas; + + char* filename; + + int last_line_style; + int last_fill_mode; + FILE* file; +};</pre> +<p>Then it must implement the cdcreatecanvas and cdinittable functions:</p> +<pre>/* In the driver implementation file */ + +static void cdcreatecanvas(cdCanvas *canvas, void *data) +{ + cdCtxCanvas* ctxcanvas = (cdCtxCanvas *)malloc(sizeof(cdCtxCanvas)); + + // parse data parameters + ... + + ctxcanvas->canvas = canvas; + canvas->ctxcanvas = ctxcanvas; + + /* update canvas context */ + canvas->w = (int)(w_mm * res); + canvas->h = (int)(h_mm * res); + canvas->w_mm = w_mm; + canvas->h_mm = h_mm; + canvas->bpp = 24; + canvas->xres = res; + canvas->yres = res; +} + +static void cdinittable(cdCanvas* canvas) +{ + canvas->Flush = cdflush; + canvas->Clear = cdclear; + canvas->Pixel = cdpixel; + canvas->Line = cdline; + canvas->Poly = cdpoly; + ... + } + +static cdContext cdMetafileContext = +{ + CD_CAP_ALL & ~(CD_CAP_GETIMAGERGB|CD_CAP_IMAGESRV|CD_CAP_REGION|CD_CAP_FONTDIM|CD_CAP_TEXTSIZE), + cdcreatecanvas, + cdinittable, + cdplay, + cdregistercallback, +}; + +cdContext* cdContextMetafile(void) +{ + return &cdMetafileContext; +}</pre> +<p>To simplify driver administration, the context structure's linking is done as follows:</p> + + <pre>/* In the header file */ +#define <b>CD_METAFILE</b> <b><i>cdContextMetafile() +</i>cdContext</b>* <b><i>cdContextMetafile</i></b>(void) +</pre> + + + + +<h3>Attributes</h3> + + + <p>The query mechanism of an attribute is done in the core and does not + depends on the driver. Due to this fact, the attributes which are modified several times for the same + value are not updated in the drivers, thus saving processing. Similarly, if an attribute + modification in a driver was not successful, its value is not updated. Nevertheless, the + fact that a driver does not implement the attribute's modification function does not mean + that it rejects that attribute - the driver just does not need to do anything with this + attribute on that moment and will query it later, before drawing the primitive.</p> + <p>The creation of customized attributes for each driver is made generically, using + string-like attributes. A structure with the attribute's name and its <em>set</em> and <em>get</em> + functions must be declared, as in the example below:</p> + + <pre>static void set_fill_attrib(cdCtxCanvas* ctxcanvas, char* data) +{ + ctxcanvas->fill_attrib[0] = data[0]; +} + +static char* get_fill_attrib(cdCtxCanvas* ctxcanvas) +{ + return ctxcanvas->fill_attrib; +} + +static cdAttribute fill_attrib = +{ + "SIMPENFILLPOLY", + set_fill_attrib, + get_fill_attrib +}; </pre> + + <p>At <em>createcanvas</em> in the driver: </p> + + <pre>ctxcanvas->fill_attrib[0] = '1'; +ctxcanvas->fill_attrib[1] = 0; + +cdRegisterAttribute(canvas, &fill_attrib);</pre> + + <p>, for instance, must exist, thus initializing the attribute and registering it in the + canvas' attribute list.</p> + + +</body> +</html> |