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improved png export #1669

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merged 1 commit into from
Apr 5, 2023
Merged

improved png export #1669

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4 changes: 4 additions & 0 deletions lua/core/screen.lua
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Original file line number Diff line number Diff line change
Expand Up @@ -309,6 +309,10 @@ _norns.screen_circle = function(x, y, r)
_norns.screen_arc(x, y, r, 0, math.pi*2)
end

--- export png
-- @param filename: saved to dust/data/(script)/(filename).png
Screen.export_png = function(filename) _norns.screen_export_png(norns.state.data..filename..'.png') end

--- display png
-- @param filename
-- @tparam number x x position
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33 changes: 32 additions & 1 deletion matron/src/hardware/screen.c
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Expand Up @@ -396,7 +396,38 @@ double *screen_text_extents(const char *s) {

extern void screen_export_png(const char *s) {
CHECK_CR
cairo_surface_write_to_png(surface, s);
static cairo_surface_t *png;
static cairo_t *temp; // for bg fill
// width = 640 (128*4 pixels with 64 pixel black border)
// hieght = 384 (64*4 pixels plus border)
png = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 640, 384);
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@tlubke tlubke Mar 29, 2023 •
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I know I wasn't requested to review this, but I was poking around open PRs anyway. You may be able to use CAIRO_FORMAT_RGB24 and then you wouldn't have to worry about the alpha channel (pixels still fit into a uint32). That could probably allow you to lose the fill area of the code, and the bitwise OR with 0xFF for alpha.

Have you experimented with cairo_scale()? You might be able to copy the image data from surface, use create_image_surface_for_data() with the new dimensions, then apply translate and scale transformations.

EDIT: I see that PNG has a gamma metadata field, but depending on the viewing program that might not have any effect. Will it be important to match gamma in future display settings to screenshots here?

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thanks for taking a look! your suggestions make a ton of sense.

honestly all of my experience with graphics is on raw framebuffers... hence the low-level implementation. i'll see if i can find a minute to try out some of these ideas.

temp = cairo_create(png);
// fill
cairo_set_source_rgb(temp, 0, 0, 0);
cairo_rectangle(temp, 0, 0, 640, 384);
cairo_fill(temp);
// copy big pixles
uint32_t *src = (uint32_t *)cairo_image_surface_get_data(surface);
uint32_t *dst = (uint32_t *)cairo_image_surface_get_data(png);
if (!src || !dst) return;
dst += 64 + 640*64;
for(int y=0;y<64;y++) {
for(int x=0;x<128;x++) {
// FIXME: needs some sort of gamma correction?
uint32_t p = *src++ | 0xFF000000; // FF for alpha
for(int xx=0;xx<4;xx++) {
*(dst+1920) = p;
*(dst+1280) = p;
*(dst+640) = p;
*dst++ = p;
}
}
dst += 640*4 - 128*4;
}
// cleanup
cairo_destroy(temp);
cairo_surface_write_to_png(png, s);
cairo_surface_destroy((cairo_surface_t *)png);
}

void screen_display_png(const char *filename, double x, double y) {
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