How to draw images with rawfb?

[sjg20]

I am trying out Nuklear on a raw frame buffer (boot loader environment - U-Boot).

I can see examples of how to create an nk_image and draw it for openGL, but I cannot figure out how it works with nuklear_rawfb.h

It seems to draw fonts but I am not sure how to make it draw images. Is there an example?

[seanpringle]

I think nk_rawfb_drawimage is incomplete since &rawfb->font_text is hard coded:

https://github.com/Immediate-Mode-UI/Nuklear/blob/master/demo/x11_rawfb/nuklear_rawfb.h#L1010

I hacked around it like this to make an nk_image_ptr() test work:

NK_API void
nk_rawfb_drawimage(const struct rawfb_context *rawfb,
	const int x, const int y, const int w, const int h,
	const struct nk_image *img, const struct nk_color *col)
{
	struct nk_rect src_rect;
	struct nk_rect dst_rect;

	src_rect.x = img->region[0];
	src_rect.y = img->region[1];
	src_rect.w = img->region[2];
	src_rect.h = img->region[3];

	dst_rect.x = x;
	dst_rect.y = y;
	dst_rect.w = w;
	dst_rect.h = h;

	if (img->handle.ptr == NULL) { // probably a dangerous assumption?
		nk_rawfb_stretch_image(&rawfb->fb, &rawfb->font_tex, &dst_rect, &src_rect, &rawfb->scissors, col);
		return;
	}

	struct rawfb_image rimg = {
		.pixels = img->handle.ptr,
		.w = img->w,
		.h = img->h,
		.pitch = img->w*sizeof(uint32_t),
		.pl = PIXEL_LAYOUT_XBGR_8888,
		.format = NK_FONT_ATLAS_RGBA32,
	};

	nk_rawfb_stretch_image(&rawfb->fb, &rimg, &dst_rect, &src_rect, &rawfb->scissors, &nk_none);
}

Then using it:

void *ptr = <raw RGBA buffer>;
struct nk_image img = nk_image_ptr(ptr);
img.w = w;
img.h = h;
img.region[2] = w;
img.region[3] = h;
nk_image(&ctx, img);

Other bits that tripped me up for a while:

• Pay attention to how nk_rawfb_int2color handles byte order on the target platform. The PIXEL_LAYOUT_XBGR_8888 above was necessary for my colors to appear correctly, but YMMV.
• nk_rawfb_stretch_image overrides foreground color which is fine for font and buttons, but not for actual images. I had to tweak it to optionally disable the foreground color and transfer pixels unchanged except for alpha blending.
• struct nk_image doesn't allow passing through a pitch value even though struct rawfb_image does support it. So make sure pitch == w*sizeof(uint32).

[dumblob]

This is great feedback! Could you please make a PR with the suggestions and findings?

The backends are mainly for demonstration purposes as everybody has slightly different needs. Therefore they might be incomplete or less tested. Our main focus is on the library itself (just nuklear.h), which is backend-agnostic (see our new reviewers guide in readme 😉).

[seanpringle]

Will do, but I've hacked around elsewhere too, such as extending nk_rawfb_init for loading other fonts, and adding an endianness check. Something PR-worthy may come out of it eventually!

In my case rawfb is drawing directly to an SDL2 streaming texture, which is then displayed over a window background drawn with the vanilla SDL2 renderer.

[seanpringle]

Fwiw, I've failed to get around to doing a PR for rawfb and probably won't now, sorry. Ended up replacing most of the rawfb code with Cairo software rendering: https://github.com/seanpringle/nuklear_cairo

[dumblob]

No problem.

Btw. feel free to make a PR with x11-cairo backend (or wayland-cairo - didn't look at the source, so don't know which one 😉) - we're not strict about backend implementations and merge anything what makes sense for future users. Cairo is certainly an interesting backend!