Hxcpp windows target:: need help with Pointers.

[Tom]

Hi!

I try to port the original example of NanoVG into Michael Bickel's hx-nanovg lib with Haxe, Hxcpp windows platform. It's going well, but...

There is a function in C++:

// Breaks the specified text into lines. If end is specified only the sub-string will be used.
// White space is stripped at the beginning of the rows, the text is split at word boundaries or when new-line characters are encountered.
// Words longer than the max width are slit at nearest character (i.e. no hyphenation).
int nvgTextBreakLines(NVGcontext* ctx, const char* string, const char* end, float breakRowWidth, NVGtextRow* rows, int maxRows);

// the used structure
struct NVGtextRow {
    const char* start;    // Pointer to the input text where the row starts.
    const char* end;    // Pointer to the input text where the row ends (one past the last character).
    const char* next;    // Pointer to the beginning of the next row.
    float width;        // Logical width of the row.
    float minx, maxx;    // Actual bounds of the row. Logical with and bounds can differ because of kerning and some parts over extending.
};

... and in Nvg.hx the extern for this:

@:native("::nvgTextBreakLines")
public static function textBreakLines(_ctx:Pointer<NvgContext>, _string:ConstPointer<Char>, _end:ConstPointer<Char>, _breakRowWidth:Float32, _rows:Pointer<NvgTextRow>, _maxRows:Int):Int;

@:native("NVGtextRow")
extern class NvgTextRow {
    /** Pointer to the input text where the row starts. **/
    public var start:ConstPointer<Char>;
    /** Pointer to the input text where the row ends (one past the last character). **/
    public var end:ConstPointer<Char>;
    /** Pointer to the beginning of the next row. **/
    public var next:ConstPointer<Char>;
    /** Logical width of the row. **/
    public var width:Float32;
    /** Actual bounds of the row. Logical with and bounds can differ because of kerning and some parts over extending. **/
    public var minx:Float32;
    /** Actual bounds of the row. Logical with and bounds can differ because of kerning and some parts over extending. **/
    public var maxx:Float32;
}

I have a problem with the _rows:Pointer<NvgTextRow> variable, because the original code of the usage of this function is: (the comments are my interpretation, and maybe not correct)

NVGtextRow rows[3]; // create a 3 length array of NVGtextRow
nvgTextBreakLines(vg, start, end, width, rows, 3); // this function sets the rows variable

I can't create in Haxe the appropriate rows variable.
I tried:

var rows:Array<NvgTextRow>; // This will be in cpp: Array<Dynamic> type.
Nvg.textBreakLines(vg, start, end, width, Pointer.fromHandle(rows), 3); // error: can't covert Dynamic to NVGtextRow

How can I do this in the right way and pass a pointer of 3 length array? Can it be done in Hxcpp?

Thanks in advance!
Tom

[Michael Bickel]

Hi Tom,

It's a bit cunbersome but I think you can achieve this in the following way:

untyped __cpp__("NVGtextRow rows[3];");

Nvg.textBreakLines(vg, "f\nb", untyped null, 50, untyped __cpp__("rows"), 3);

var firstRow:NvgTextRow = untyped __cpp__("rows[0]");

trace(firstRow.width + " " + firstRow.minx + " " + firstRow.maxx);

Maybe Hugh can shed more light on the best practices for such a case.

- Michael 

[Tom]

Hi Michael!

Thanks for this. It's working.
There was some trickier part (for me), but working. :)



There are some linecaps which are displaying wrong with NvgLineCap.SQUARE, but the others are working.

[Tom]

The image for the previous post.

[Michael Bickel]

Hi Tom, 

Thats very nice! Good work! :)

- Michael

[Tom]

Thanks!
I created a pull request, so you could add these example to your hx-nanovg project.

By the way, there are some performance comparison how fast this library? Can we use it e.g. display, and zoom some heavy svg?

[Hugh]

Yes,the "Arrays" are not really designed for holding structures, only pointers.  Maybe I could make an exception for externs, but it would be some work.

Other possible technique would be to "new" an native array into a pointer, and delete it when you are done.

Hugh