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Refine drawing API semantics to pass drawing * instead of void *

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This changes the drawing API so that implementations receive a
`drawing *` pointer with each call, instead of a `void *` pointer as
they did previously. The `void *` context pointer has been moved to be
a member of the `drawing` structure (which has been made public), from
which it can be retrieved via the new `GET_HANDLE_AS_TYPE()` macro. To
signal this breaking change to downstream front end authors, I've
added a version number to the `drawing_api` struct, which will
hopefully force them to notice.

The motivation for this change is the upcoming introduction of a
draw_polygon_fallback() function, which will use a series of calls to
draw_line() to perform software polygon rasterization on platforms
without a native polygon fill primitive. This function is fairly
large, so I desired that it not be included in the binary
distribution, except on platforms which require it (e.g. my Rockbox
port). One way to achieve this is via link-time optimization (LTO,
a.k.a. "interprocedural optimization"/IPO), so that the code is
unconditionally compiled (preventing bit-rot) but only included in the
linked executable if it is actually referenced from elsewhere.
Practically, this precludes the otherwise straightforward route of
including a run-time check of the `draw_polygon` pointer in the
drawing.c middleware. Instead, Simon recommended that a front end be
able to set its `draw_polygon` field to point to
draw_polygon_fallback(). However, the old drawing API's semantics of
passing a `void *` pointer prevented this from working in practice,
since draw_polygon_fallback(), implemented in middleware, would not be
able to perform any drawing operations without a `drawing *` pointer;
with the new API, this restriction is removed, clearing the way for
that function's introduction.

This is a breaking change for front ends, which must update their
implementations of the drawing API to conform. The migration process
is fairly straightforward: every drawing API function which previously
took a `void *` context pointer should be updated to take a `drawing *`
pointer in its place. Then, where each such function would have
previously casted the `void *` pointer to a meaningful type, they now
instead retrieve the context pointer from the `handle` field of the
`drawing` structure. To make this transition easier, the
`GET_HANDLE_AS_TYPE()` macro is introduced to wrap the context pointer
retrieval (see below for usage).

As an example, an old drawing API function implementation would have
looked like this:

void frontend_draw_func(void *handle, ...)
{
    frontend *fe = (frontend *)handle;
    /* do stuff with fe */
}

After this change, that function would be rewritten as:

void frontend_draw_func(drawing *dr, ...)
{
    frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
    /* do stuff with fe */
}

I have already made these changes to all the in-tree front ends, but
out-of-tree front ends will need to follow the procedure outlined
above.

Simon pointed out that changing the drawing API function pointer
signatures to take `drawing *` instead of `void *` results only in a
compiler warning, not an outright error. Thus, I've introduced a
version field to the beginning of the `drawing_api` struct, which will
cause a compilation error and hopefully force front ends to notice
this. This field should be set to 1 for now. Going forward, it will
provide a clear means of communicating future breaking API changes.
This commit is contained in:
Franklin Wei
2024-08-11 19:28:35 -04:00
committed by Simon Tatham
parent a993fd45eb
commit f37913002a
11 changed files with 459 additions and 342 deletions
Download Patch File Download Diff File Expand all files Collapse all files

89
gtk.c
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@ -329,9 +329,9 @@ void frontend_default_colour(frontend *fe, float *output)
output[0] = output[1] = output[2] = 0.9F;
}
static void gtk_status_bar(void *handle, const char *text)
static void gtk_status_bar(drawing *dr, const char *text)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
if (fe->headless)
return;
@ -1164,9 +1164,9 @@ static void align_and_draw_text(int index, int align, int x, int y,
* The exported drawing functions.
*/
static void gtk_start_draw(void *handle)
static void gtk_start_draw(drawing *dr)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
fe->bbox_l = fe->w;
fe->bbox_r = 0;
fe->bbox_u = fe->h;
@ -1174,23 +1174,23 @@ static void gtk_start_draw(void *handle)
setup_drawing(fe);
}
static void gtk_clip(void *handle, int x, int y, int w, int h)
static void gtk_clip(drawing *dr, int x, int y, int w, int h)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
do_clip(fe, x, y, w, h);
}
static void gtk_unclip(void *handle)
static void gtk_unclip(drawing *dr)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
do_unclip(fe);
}
static void gtk_draw_text(void *handle, int x, int y, int fonttype,
static void gtk_draw_text(drawing *dr, int x, int y, int fonttype,
int fontsize, int align, int colour,
const char *text)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
int i;
/*
@ -1220,45 +1220,45 @@ static void gtk_draw_text(void *handle, int x, int y, int fonttype,
align_and_draw_text(fe, i, align, x, y, text);
}
static void gtk_draw_rect(void *handle, int x, int y, int w, int h, int colour)
static void gtk_draw_rect(drawing *dr, int x, int y, int w, int h, int colour)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
fe->dr_api->set_colour(fe, colour);
do_draw_rect(fe, x, y, w, h);
}
static void gtk_draw_line(void *handle, int x1, int y1, int x2, int y2,
static void gtk_draw_line(drawing *dr, int x1, int y1, int x2, int y2,
int colour)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
fe->dr_api->set_colour(fe, colour);
do_draw_line(fe, x1, y1, x2, y2);
}
static void gtk_draw_thick_line(void *handle, float thickness,
static void gtk_draw_thick_line(drawing *dr, float thickness,
float x1, float y1, float x2, float y2,
int colour)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
fe->dr_api->set_colour(fe, colour);
do_draw_thick_line(fe, thickness, x1, y1, x2, y2);
}
static void gtk_draw_poly(void *handle, const int *coords, int npoints,
static void gtk_draw_poly(drawing *dr, const int *coords, int npoints,
int fillcolour, int outlinecolour)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
do_draw_poly(fe, coords, npoints, fillcolour, outlinecolour);
}
static void gtk_draw_circle(void *handle, int cx, int cy, int radius,
static void gtk_draw_circle(drawing *dr, int cx, int cy, int radius,
int fillcolour, int outlinecolour)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
do_draw_circle(fe, cx, cy, radius, fillcolour, outlinecolour);
}
static blitter *gtk_blitter_new(void *handle, int w, int h)
static blitter *gtk_blitter_new(drawing *dr, int w, int h)
{
blitter *bl = snew(blitter);
setup_blitter(bl, w, h);
@ -1267,23 +1267,23 @@ static blitter *gtk_blitter_new(void *handle, int w, int h)
return bl;
}
static void gtk_blitter_free(void *handle, blitter *bl)
static void gtk_blitter_free(drawing *dr, blitter *bl)
{
teardown_blitter(bl);
sfree(bl);
}
static void gtk_blitter_save(void *handle, blitter *bl, int x, int y)
static void gtk_blitter_save(drawing *dr, blitter *bl, int x, int y)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
do_blitter_save(fe, bl, x, y);
bl->x = x;
bl->y = y;
}
static void gtk_blitter_load(void *handle, blitter *bl, int x, int y)
static void gtk_blitter_load(drawing *dr, blitter *bl, int x, int y)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
if (x == BLITTER_FROMSAVED && y == BLITTER_FROMSAVED) {
x = bl->x;
y = bl->y;
@ -1291,18 +1291,18 @@ static void gtk_blitter_load(void *handle, blitter *bl, int x, int y)
do_blitter_load(fe, bl, x, y);
}
static void gtk_draw_update(void *handle, int x, int y, int w, int h)
static void gtk_draw_update(drawing *dr, int x, int y, int w, int h)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
if (fe->bbox_l > x ) fe->bbox_l = x ;
if (fe->bbox_r < x+w) fe->bbox_r = x+w;
if (fe->bbox_u > y ) fe->bbox_u = y ;
if (fe->bbox_d < y+h) fe->bbox_d = y+h;
}
static void gtk_end_draw(void *handle)
static void gtk_end_draw(drawing *dr)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
teardown_drawing(fe);
@ -1324,7 +1324,7 @@ static void gtk_end_draw(void *handle)
}
#ifdef USE_PANGO
static char *gtk_text_fallback(void *handle, const char *const *strings,
static char *gtk_text_fallback(drawing *dr, const char *const *strings,
int nstrings)
{
/*
@ -1336,20 +1336,20 @@ static char *gtk_text_fallback(void *handle, const char *const *strings,
#endif
#ifdef USE_PRINTING
static void gtk_begin_doc(void *handle, int pages)
static void gtk_begin_doc(drawing *dr, int pages)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
gtk_print_operation_set_n_pages(fe->printop, pages);
}
static void gtk_begin_page(void *handle, int number)
static void gtk_begin_page(drawing *dr, int number)
{
}
static void gtk_begin_puzzle(void *handle, float xm, float xc,
static void gtk_begin_puzzle(drawing *dr, float xm, float xc,
float ym, float yc, int pw, int ph, float wmm)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
double ppw, pph, pox, poy, dpmmx, dpmmy;
double scale;
@ -1385,29 +1385,29 @@ static void gtk_begin_puzzle(void *handle, float xm, float xc,
fe->hatchspace = 1.0 * pw / wmm;
}
static void gtk_end_puzzle(void *handle)
static void gtk_end_puzzle(drawing *dr)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
cairo_restore(fe->cr);
}
static void gtk_end_page(void *handle, int number)
static void gtk_end_page(drawing *dr, int number)
{
}
static void gtk_end_doc(void *handle)
static void gtk_end_doc(drawing *dr)
{
}
static void gtk_line_width(void *handle, float width)
static void gtk_line_width(drawing *dr, float width)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
cairo_set_line_width(fe->cr, width);
}
static void gtk_line_dotted(void *handle, bool dotted)
static void gtk_line_dotted(drawing *dr, bool dotted)
{
frontend *fe = (frontend *)handle;
frontend *fe = GET_HANDLE_AS_TYPE(dr, frontend);
if (dotted) {
const double dash = 35.0;
@ -1435,6 +1435,7 @@ static const struct internal_drawing_api internal_printing = {
#endif
static const struct drawing_api gtk_drawing = {
1,
gtk_draw_text,
gtk_draw_rect,
gtk_draw_line,