Hello Thomas,
Thanks a lot for your feedback.
On 2/4/22 16:52, Thomas Zimmermann wrote:
[snip]
+static void drm_fb_gray8_to_mono_reversed_line(u8 *dst, const u8 *src, size_t pixels)
+{
+ unsigned int xb, i;
+
+ for (xb = 0; xb < pixels / 8; xb++) {
In practice, all mode widths are multiples of 8 because VGA mandated it.
So it's ok-ish to assume this here. You should probably at least print a
warning somewhere if (pixels % 8 != 0)
Agreed.
[snip]
+ * DRM doesn't have native monochrome or grayscale support.
+ * Such drivers can announce the commonly supported XR24 format to userspace
+ * and use drm_fb_xrgb8888_to_gray8() to convert to grayscale and then this
+ * helper function to convert to the native format.
+ */
+void drm_fb_gray8_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *src,
+ const struct drm_rect *clip)
There's a bug here. You want to pass in a drm_framebuffer as fourth
argument.
+{
+
+ size_t height = drm_rect_height(clip);
+ size_t width = drm_rect_width(clip);
+ unsigned int y;
+ const u8 *gray8 = src;
+ u8 *mono = dst;
+
+ if (!dst_pitch)
+ dst_pitch = width;
The dst_pitch is given in bytes. You have to device by 8. Here would be
a good place to warn if (width % 8 != 0).
Ok.
+
+ for (y = 0; y < height; y++) {
+ drm_fb_gray8_to_mono_reversed_line(mono, gray8, dst_pitch);
+ mono += (dst_pitch / 8);
The dst_pitch is already given in bytes.
Yes, I know but for reversed mono we want only 1/8 of the width since we
are converting from 8 bits per pixel greyscale to 1 bit per pixel mono.
Or am I misunderstanding what you meant ?
+ gray8 += dst_pitch;
'gray8 += fb->pitches[0]' would be correct.
Ok.
[snip]
+ */
+void drm_fb_xrgb8888_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *src,
+ const struct drm_framebuffer *fb,
+ const struct drm_rect *clip)
+{
+ if (WARN_ON(fb->format->format != DRM_FORMAT_XRGB8888))
+ return;
+
+ if (!dst_pitch)
+ dst_pitch = drm_rect_width(clip);
+
+ drm_fb_xrgb8888_to_gray8(dst, dst_pitch, src, fb, clip);
+ drm_fb_gray8_to_mono_reversed(dst, dst_pitch, dst, fb, clip);
Converting from dst into dst can give incorrect results. At some point
we probably want to add restrict qualifiers to these pointers, to help
the compiler with optimizing.
A better approach here is to pull the per-line conversion from
drm_fb_xrgb8888_to_gray8() into a separate helper and implement a
line-by-line conversion here. something like this:
drm_fb_xrgb8888_to_mono_reversed()
{
char *tmp = kmalloc(size of a single line of gray8)
for (heigth) {
drm_fb_xrgb8888_to_gray8_line(tmp, ..., src, ...);
drm_fb_gray8_to_mono_reversed(dst, ..., tmp, ...);
src += fb->pitches[0]
dst += dst_pitch;
}
kfree(tmp);
}
I see. Yes, that sounds a much better approach. I'll change it in v3.
Best regards,
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