SVG defines vector-based graphics in XML format (a markup language that defines a set of rules for encoding documents in a format which is both human-readable and machine-readable), so SVG files content can be represented as a C string.
Here is a standard C function able to load an SVG file and return a pointer to its content:
char* loadXml(const char* fileName) {
char* buffer;
size_t size, read;
FILE* fp = NULL;
#if defined(_MSC_VER) && (_MSC_VER >= 1400 )
/* make Microsoft Visual Studio happy */
errno_t err = fopen_s(&fp, fileName, "rb");
if ((fp == NULL) || (err != 0)) {
#else
fp = fopen(fileName, "rb");
if (fp == NULL) {
#endif
return NULL;
}
fseek(fp, 0, SEEK_SET);
fgetc(fp);
if (ferror(fp) != 0) {
fclose(fp);
return NULL;
}
/* get the file size */
fseek(fp, 0, SEEK_END);
size = ftell(fp);
fseek(fp, 0, SEEK_SET);
if (size == 0) {
fclose(fp);
return NULL;
}
/* allocate a memory buffer equal to the file size */
/* plus an additional character for the trailing '\0' */
buffer = calloc(size + 1, sizeof(char));
if (buffer == NULL) {
fclose(fp);
return NULL;
}
/* read the file content and store it within the memory buffer */
read = fread(buffer, sizeof(char), size, fp);
if (read != size) {
free(buffer);
fclose(fp);
return NULL;
}
/* close the file and return the pointer to the memory buffer */
fclose(fp);
return buffer;
}
SVGTHandle loadSvg(const char* fileName) {
SVGTHandle svgHandle = SVGT_INVALID_HANDLE;
if (fileName != NULL) {
/* allocate buffer and load file */
char* buffer = (char *)loadXml(fileName);
if (buffer != NULL) {
/* create the SVG document */
svgHandle = svgtDocCreate(buffer);
/* free the allocated buffer */
free(buffer);
}
}
return svgHandle;
}
In order to render SVG contents, AmanithSVG must create an optimized in-memory representation of SVG files: a such representation is called an SVG document. It is possible to create an SVG document given its C string representation using the svgtDocCreate function:
/*
Create and load an SVG document, specifying the whole XML string.
Return SVGT_INVALID_HANDLE in case of errors, else a valid document handle.
*/
SVGTHandle svgtDocCreate(const char* xmlText);
So, for example, in order to let AmanithSVG to render the userInterface.svg file, it is possible to create the relative SVG document as follow:
SVGTHandle svgDoc = loadSvg("userInterface.svg");
When an SVG document is no longer necessary, its resources can be freed using the svgtDocDestroy function:
/*
Destroy a previously created SVG document.
Return SVGT_NO_ERROR if the operation was completed successfully, else an
error code.
*/
SVGTErrorCode svgtDocDestroy(SVGTHandle svgDoc);
SVG files themself optionally can provide information about the appropriate viewport region for the content via the width and height XML attributes on the outermost <svg> element. Once that an SVG document has been created, the following functions could be used to retrieve the suggested viewport width/height, in pixels:
/*
It returns a negative number (i.e. an invalid width) in the following cases:
- the library has not previously been initialized through the svgtInit
function
- outermost element is not an <svg> element
- outermost <svg> element doesn't have a 'width' attribute specified
- outermost <svg> element has a negative 'width' attribute specified
(e.g. width="-50")
- outermost <svg> element has a 'width' attribute specified
in relative measure units (i.e. em, ex, % percentage)
In all such cases the last-error code will be set to SVGT_INVALID_SVG_ERROR.
*/
SVGTfloat svgtDocWidth(SVGTHandle svgDoc);
/*
It returns a negative number (i.e. an invalid height) in the following cases:
- the library has not previously been initialized through the svgtInit
function
- outermost element is not an <svg> element
- outermost <svg> element doesn't have a 'height' attribute specified
- outermost <svg> element has a negative 'height' attribute specified
(e.g. height="-30")
- outermost <svg> element has a 'height' attribute specified in
relative measure units (i.e. em, ex, % percentage)
In all such cases the last-error code will be set to SVGT_INVALID_SVG_ERROR.
*/
SVGTfloat svgtDocHeight(SVGTHandle svgDoc);