libpayload: cbgfx: Add draw_line()

Add a function draw_line() to draw either a horizontal or vertical line
segment.

Theoretically a horizontal line can also be drawn by calling
draw_rounded_box() with dim_rel.x being the line length and dim_rel.y
being the line width. However, due to the truncation in integer division
when converting relative coordinates to absolute ones, this will
potentially produce inconsistent line widths, depending on the value of
pos_rel.y.

It is guaranteed that draw_line() will produce consistent line widths,
regardless of the position of the line. Also, when the thickness
argument is zero, this function is able to draw a line with 1-pixel
width, which is not achievable by draw_rounded_box().

BRANCH=puff
BUG=b:146399181, b:161424726
TEST=emerge-puff libpayload

Change-Id: I2d50414c4bfed343516197da9bb50791c89ba4c2
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43508
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Joel Kitching <kitching@google.com>

payloads/libpayload/drivers/video/graphics.c

@@ -99,6 +99,11 @@ static void add_vectors(struct vector *out,
 	out->y = v1->y + v2->y;
 }
 
+static int fraction_equal(const struct fraction *f1, const struct fraction *f2)
+{
+	return (int64_t)f1->n * f2->d == (int64_t)f2->n * f1->d;
+}
+
 static int is_valid_fraction(const struct fraction *f)
 {
 	return f->d != 0;
@@ -109,17 +114,31 @@ static int is_valid_scale(const struct scale *s)
 	return is_valid_fraction(&s->x) && is_valid_fraction(&s->y);
 }
 
+static void reduce_fraction(struct fraction *out, int64_t n, int64_t d)
+{
+	/* Simplest way to reduce the fraction until fitting in int32_t */
+	int shift = log2(MAX(ABS(n), ABS(d)) >> 31) + 1;
+	out->n = n >> shift;
+	out->d = d >> shift;
+}
+
+/* out = f1 + f2 */
 static void add_fractions(struct fraction *out,
 			  const struct fraction *f1, const struct fraction *f2)
 {
-	int64_t n, d;
+	reduce_fraction(out,
-	int shift;
+			(int64_t)f1->n * f2->d + (int64_t)f2->n * f1->d,
-	n = (int64_t)f1->n * f2->d + (int64_t)f2->n * f1->d;
+			(int64_t)f1->d * f2->d);
-	d = (int64_t)f1->d * f2->d;
+}
-	/* Simplest way to reduce the fraction until fitting in int32_t */
+
-	shift = log2(MAX(ABS(n), ABS(d)) >> 31) + 1;
+/* out = f1 - f2 */
-	out->n = n >> shift;
+static void subtract_fractions(struct fraction *out,
-	out->d = d >> shift;
+			       const struct fraction *f1,
+			       const struct fraction *f2)
+{
+	reduce_fraction(out,
+			(int64_t)f1->n * f2->d - (int64_t)f2->n * f1->d,
+			(int64_t)f1->d * f2->d);
 }
 
 static void add_scales(struct scale *out,
@@ -477,6 +496,59 @@ int draw_rounded_box(const struct scale *pos_rel, const struct scale *dim_rel,
 	return CBGFX_SUCCESS;
 }
 
+int draw_line(const struct scale *pos1, const struct scale *pos2,
+	      const struct fraction *thickness, const struct rgb_color *rgb)
+{
+	struct fraction len;
+	struct vector top_left;
+	struct vector size;
+	struct vector p, t;
+
+	if (cbgfx_init())
+		return CBGFX_ERROR_INIT;
+
+	const uint32_t color = calculate_color(rgb, 0);
+
+	if (!is_valid_fraction(thickness))
+		return CBGFX_ERROR_INVALID_PARAMETER;
+
+	transform_vector(&top_left, &canvas.size, pos1, &canvas.offset);
+	if (fraction_equal(&pos1->y, &pos2->y)) {
+		/* Horizontal line */
+		subtract_fractions(&len, &pos2->x, &pos1->x);
+		struct scale dim = {
+			.x = { .n = len.n, .d = len.d },
+			.y = { .n = thickness->n, .d = thickness->d },
+		};
+		transform_vector(&size, &canvas.size, &dim, &vzero);
+		size.y = MAX(size.y, 1);
+	} else if (fraction_equal(&pos1->x, &pos2->x)) {
+		/* Vertical line */
+		subtract_fractions(&len, &pos2->y, &pos1->y);
+		struct scale dim = {
+			.x = { .n = thickness->n, .d = thickness->d },
+			.y = { .n = len.n, .d = len.d },
+		};
+		transform_vector(&size, &canvas.size, &dim, &vzero);
+		size.x = MAX(size.x, 1);
+	} else {
+		LOG("Only support horizontal and vertical lines\n");
+		return CBGFX_ERROR_INVALID_PARAMETER;
+	}
+
+	add_vectors(&t, &top_left, &size);
+	if (within_box(&t, &canvas) < 0) {
+		LOG("Line exceeds canvas boundary\n");
+		return CBGFX_ERROR_BOUNDARY;
+	}
+
+	for (p.y = top_left.y; p.y < t.y; p.y++)
+		for (p.x = top_left.x; p.x < t.x; p.x++)
+			set_pixel(&p, color);
+
+	return CBGFX_SUCCESS;
+}
+
 int clear_canvas(const struct rgb_color *rgb)
 {
 	const struct rect box = {

payloads/libpayload/include/cbgfx.h

@@ -132,6 +132,22 @@ int draw_rounded_box(const struct scale *pos_rel, const struct scale *dim_rel,
 		     const struct fraction *thickness,
 		     const struct fraction *radius);
 
+/**
+ * Draw a horizontal or vertical line segment on screen. If horizontal, pos1
+ * must be the left endpoint. If vertical, pos1 must be the top endpoint. When
+ * the specified thickness is zero (or truncated to zero), a line with 1-pixel
+ * width will be drawn.
+ *
+ * @param[in] pos1	Start position of the line relative to the canvas.
+ * @param[in] pos2	End position of the line relative to the canvas.
+ * @param[in] thickness Thickness of the line relative to the canvas.
+ * @param[in] rgb       Color of the line.
+ *
+ * @return CBGFX_* error codes
+ */
+int draw_line(const struct scale *pos1, const struct scale *pos2,
+	      const struct fraction *thickness, const struct rgb_color *rgb);
+
 /**
  * Clear the canvas
  */