[coreboot-gerrit] Change in coreboot[master]: libpayload: cbgfx: Fix 'equals' counter for Lanczos resampling

[Yu-Ping Wu (Code Review)]

Yu-Ping Wu has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/45235 )

Change subject: libpayload: cbgfx: Fix 'equals' counter for Lanczos resampling
......................................................................

libpayload: cbgfx: Fix 'equals' counter for Lanczos resampling

The 'equals' counter stores the number of latest pixels that were
exactly equal. Since the sample array is updated in a column-based
manner, we should also initialize the 'equals' counter in the same
order.

BUG=b:167739127
TEST=emerge-puff libpayload
TEST=Character 'k' is rendered correctly on puff
BRANCH=zork

Change-Id: Ibc91ad1af85adcf093eff40797cd54f32f57111d
Signed-off-by: Yu-Ping Wu 
---
M payloads/libpayload/drivers/video/graphics.c
1 file changed, 22 insertions(+), 20 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/35/45235/1

diff --git a/payloads/libpayload/drivers/video/graphics.c b/payloads/libpayload/drivers/video/graphics.c
index 2bf5e19..a8c9612 100644
--- a/payloads/libpayload/drivers/video/graphics.c
+++ b/payloads/libpayload/drivers/video/graphics.c
@@ -858,36 +858,38 @@
    	}

/*
-		 * Initialize the sample array for this line. For pixels to the
-		 * left of S0 there are no corresponding input pixels so just
-		 * copy the S0 values over.
-		 *
-		 * Also initialize the equals counter, which counts how many of
-		 * the latest pixels were exactly equal. We know the columns
-		 * left of S0 must be equal to S0, so start with that number.
+		 * Initialize the sample array for this line, and also
+		 * the equals counter, which counts how many of the latest
+		 * pixels were exactly equal.
    	 */
-		int equals = S0 * SSZ;
-		uint8_t last_equal = ypix[0][0];
-		for (sy = 0; sy < SSZ; sy++) {
-			for (sx = S0; sx < SSZ; sx++) {
+		int equals = 0;
+		uint8_t last_equal = -1;
+		struct rgb_color *last_sample = NULL;
+		for (sx = 0; sx < SSZ; sx++) {
+			for (sy = 0; sy < SSZ; sy++) {
    			if (sx >= dim_org->width) {
    				sample[sx][sy] = sample[sx - 1][sy];
    				equals++;
    				continue;
    			}
-				uint8_t i = ypix[sy][sx - S0];
+				/*
+				 * For pixels to the left of S0 there are no
+				 * corresponding input pixels so just use
+				 * ypix[sy][0].
+				 */
+				uint8_t i = ypix[sy][MAX(0, sx - S0)];
+				if (last_sample && i == last_equal) {
+					sample[sx][sy] = *last_sample;
+					equals++;
+					continue;
+				}
    			if (pal_to_rgb(i, pal, header->colors_used,
    				       &sample[sx][sy]))
    				goto bitmap_error;
-				if (i == last_equal) {
-					equals++;
-				} else {
-					last_equal = i;
-					equals = 1;
-				}
+				last_equal = i;
+				last_sample = &sample[sx][sy];
+				equals = 1;
    		}
-			for (sx = S0 - 1; sx >= 0; sx--)
-				sample[sx][sy] = sample[S0][sy];
    	}

ix = 0;