util: add SMPTE pattern support for C1 format

Add support for drawing the SMPTE pattern in a buffer using the C1
indexed format.

As only two colors are available, the pattern is drawn in black and
white, using Floyd-Steinberg dithering[1].

[1] https://en.wikipedia.org/wiki/Floyd%E2%80%93Steinberg_dithering

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---
Dithering example at https://drive.google.com/file/d/1waJczErrIaEKRhBCCU1ynxRG8agpo0Xx/view

v5:
  - Add Reviewed-by,

v4:
  - Replace FILL_COLOR() use by bw_color_lut[],

v3:
  - Add Acked-by,
  - Add Wikipedia link,

v2:
  New.

tests/util/pattern.c

@@ -654,6 +654,11 @@ static unsigned int smpte_bottom[8] = {
 
 #define EXPAND_COLOR(r, g, b)	{ (r) * 0x101, (g) * 0x101, (b) * 0x101 }
 
+static const struct drm_color_lut bw_color_lut[] = {
+	EXPAND_COLOR(  0,   0,   0),	/* black */
+	EXPAND_COLOR(255, 255, 255),	/* white */
+};
+
 static const struct drm_color_lut smpte_color_lut[] = {
 	[SMPTE_COLOR_GREY] =        EXPAND_COLOR(192, 192, 192),
 	[SMPTE_COLOR_YELLOW] =      EXPAND_COLOR(192, 192,   0),
@@ -672,6 +677,164 @@ static const struct drm_color_lut smpte_color_lut[] = {
 
 #undef EXPAND_COLOR
 
+/*
+ * Floyd-Steinberg dithering
+ */
+
+struct fsd {
+	unsigned int width;
+	unsigned int x;
+	unsigned int i;
+	int red;
+	int green;
+	int blue;
+	int error[];
+};
+
+static struct fsd *fsd_alloc(unsigned int width)
+{
+	unsigned int n = 3 * (width + 1);
+	struct fsd *fsd = malloc(sizeof(*fsd) + n * sizeof(fsd->error[0]));
+
+	fsd->width = width;
+	fsd->x = 0;
+	fsd->i = 0;
+	memset(fsd->error, 0, n * sizeof(fsd->error[0]));
+
+	return fsd;
+}
+
+static inline int clamp(int val, int min, int max)
+{
+	if (val < min)
+		return min;
+	if (val > max)
+		return max;
+	return val;
+}
+
+static void fsd_dither(struct fsd *fsd, struct drm_color_lut *color)
+{
+	unsigned int i = fsd->i;
+
+	fsd->red = (int)color->red + (fsd->error[3 * i] + 8) / 16;
+	fsd->green = (int)color->green + (fsd->error[3 * i + 1] + 8) / 16;
+	fsd->blue = (int)color->blue + (fsd->error[3 * i + 2] + 8) / 16;
+
+	color->red = clamp(fsd->red, 0, 65535);
+	color->green = clamp(fsd->green, 0, 65535);
+	color->blue = clamp(fsd->blue, 0, 65535);
+}
+
+static void fsd_update(struct fsd *fsd, const struct drm_color_lut *actual)
+{
+	int error_red = fsd->red - (int)actual->red;
+	int error_green = fsd->green - (int)actual->green;
+	int error_blue = fsd->blue - (int)actual->blue;
+	unsigned int width = fsd->width;
+	unsigned int i = fsd->i, j;
+	unsigned int n = width + 1;
+
+	/* Distribute errors over neighboring pixels */
+	if (fsd->x == width - 1) {
+		/* Last pixel on this scanline */
+		/* South East: initialize to zero */
+		fsd->error[3 * i] = 0;
+		fsd->error[3 * i + 1] = 0;
+		fsd->error[3 * i + 2] = 0;
+	} else {
+		/* East: accumulate error */
+		j = (i + 1) % n;
+		fsd->error[3 * j] += 7 * error_red;
+		fsd->error[3 * j + 1] += 7 * error_green;
+		fsd->error[3 * j + 2] += 7 * error_blue;
+
+		/* South East: initial error */
+		fsd->error[3 * i] = error_red;
+		fsd->error[3 * i + 1] = error_green;
+		fsd->error[3 * i + 2] = error_blue;
+	}
+	/* South West: accumulate error */
+	j = (i + width - 1) % n;
+	fsd->error[3 * j] += 3 * error_red;
+	fsd->error[3 * j + 1] += 3 * error_green;
+	fsd->error[3 * j + 2] += 3 * error_blue;
+
+	/* South: accumulate error */
+	j = (i + width) % n;
+	fsd->error[3 * j] += 5 * error_red;
+	fsd->error[3 * j + 1] += 5 * error_green;
+	fsd->error[3 * j + 2] += 5 * error_blue;
+
+	fsd->x = (fsd->x + 1) % width;
+	fsd->i = (fsd->i + 1) % n;
+}
+
+static void write_pixel_1(uint8_t *mem, unsigned int x, unsigned int pixel)
+{
+	unsigned int shift = 7 - (x & 7);
+	unsigned int mask = 1U << shift;
+
+	mem[x / 8] = (mem[x / 8] & ~mask) | ((pixel << shift) & mask);
+}
+
+static void write_color_1(struct fsd *fsd, uint8_t *mem, unsigned int x,
+			  unsigned int index)
+{
+	struct drm_color_lut color = smpte_color_lut[index];
+	unsigned int pixel;
+
+	fsd_dither(fsd, &color);
+
+	/* ITU BT.601: Y = 0.299 R + 0.587 G + 0.114 B */
+	if (3 * color.red + 6 * color.green + color.blue >= 10 * 32768) {
+		pixel = 1;
+		color.red = color.green = color.blue = 65535;
+	} else {
+		pixel = 0;
+		color.red = color.green = color.blue = 0;
+	}
+
+	fsd_update(fsd, &color);
+
+	write_pixel_1(mem, x, pixel);
+}
+
+static void fill_smpte_c1(void *mem, unsigned int width, unsigned int height,
+			  unsigned int stride)
+{
+	struct fsd *fsd = fsd_alloc(width);
+	unsigned int x;
+	unsigned int y;
+
+	for (y = 0; y < height * 6 / 9; ++y) {
+		for (x = 0; x < width; ++x)
+			write_color_1(fsd, mem, x, smpte_top[x * 7 / width]);
+		mem += stride;
+	}
+
+	for (; y < height * 7 / 9; ++y) {
+		for (x = 0; x < width; ++x)
+			write_color_1(fsd, mem, x, smpte_middle[x * 7 / width]);
+		mem += stride;
+	}
+
+	for (; y < height; ++y) {
+		for (x = 0; x < width * 5 / 7; ++x)
+			write_color_1(fsd, mem, x,
+				      smpte_bottom[x * 4 / (width * 5 / 7)]);
+		for (; x < width * 6 / 7; ++x)
+			write_color_1(fsd, mem, x,
+				      smpte_bottom[(x - width * 5 / 7) * 3 /
+						   (width / 7) + 4]);
+		for (; x < width; ++x)
+			write_color_1(fsd, mem, x, smpte_bottom[7]);
+		mem += stride;
+	}
+
+	free(fsd);
+}
+
 static void write_pixel_4(uint8_t *mem, unsigned int x, unsigned int pixel)
 {
 	if (x & 1)
@@ -746,14 +909,17 @@ static void fill_smpte_c8(void *mem, unsigned int width, unsigned int height,
 
 void util_smpte_fill_lut(unsigned int ncolors, struct drm_color_lut *lut)
 {
-	if (ncolors < ARRAY_SIZE(smpte_color_lut)) {
+	if (ncolors < ARRAY_SIZE(bw_color_lut)) {
 		printf("Error: lut too small: %u < %zu\n", ncolors,
-		       ARRAY_SIZE(smpte_color_lut));
+		       ARRAY_SIZE(bw_color_lut));
 		return;
 	}
 	memset(lut, 0, ncolors * sizeof(struct drm_color_lut));
 
-	memcpy(lut, smpte_color_lut, sizeof(smpte_color_lut));
+	if (ncolors < ARRAY_SIZE(smpte_color_lut))
+		memcpy(lut, bw_color_lut, sizeof(bw_color_lut));
+	else
+		memcpy(lut, smpte_color_lut, sizeof(smpte_color_lut));
 }
 
 static void fill_smpte(const struct util_format_info *info, void *planes[3],
@@ -763,6 +929,8 @@ static void fill_smpte(const struct util_format_info *info, void *planes[3],
 	unsigned char *u, *v;
 
 	switch (info->format) {
+	case DRM_FORMAT_C1:
+		return fill_smpte_c1(planes[0], width, height, stride);
 	case DRM_FORMAT_C4:
 		return fill_smpte_c4(planes[0], width, height, stride);
 	case DRM_FORMAT_C8: