From 13414b50373f157a6b9d695054d4d041cb5ca475 Mon Sep 17 00:00:00 2001
From: Phil Howard <phil@pimoroni.com>
Date: Wed, 14 Dec 2022 17:50:50 +0000
Subject: [PATCH] JPEGDEC: Clip drawing to iWidthUsed.

Corrects clipping width using new iWidthUsed value, noticable particularly on smaller jpegs and those that aren't a multiple of the MCU sized.

Fixes #573
---
 libraries/jpegdec/JPEGDEC.h             | 1 +
 libraries/jpegdec/jpeg.inl              | 5 ++++-
 micropython/modules/jpegdec/jpegdec.cpp | 4 ++++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/libraries/jpegdec/JPEGDEC.h b/libraries/jpegdec/JPEGDEC.h
index f49cd3b5..a3f55b8e 100644
--- a/libraries/jpegdec/JPEGDEC.h
+++ b/libraries/jpegdec/JPEGDEC.h
@@ -108,6 +108,7 @@ typedef struct jpeg_draw_tag
 {
     int x, y; // upper left corner of current MCU
     int iWidth, iHeight; // size of this MCU
+    int iWidthUsed; // clipped size for odd/edges
     int iBpp; // bit depth of the pixels (8 or 16)
     uint16_t *pPixels; // 16-bit pixels
     void *pUser;
diff --git a/libraries/jpegdec/jpeg.inl b/libraries/jpegdec/jpeg.inl
index 57c9261e..be792a25 100644
--- a/libraries/jpegdec/jpeg.inl
+++ b/libraries/jpegdec/jpeg.inl
@@ -3454,10 +3454,13 @@ static int DecodeJPEG(JPEGIMAGE *pJPEG)
             if (xoff == iPitch || x == cx-1) // time to draw
             {
                 xoff = 0;
-                jd.iWidth = iPitch; // width of each LCD block group
+                jd.iWidth = jd.iWidthUsed = iPitch; // width of each LCD block group
                 jd.pUser = pJPEG->pUser;
                 if (pJPEG->ucPixelType > EIGHT_BIT_GRAYSCALE) // dither to 4/2/1 bits
                     JPEGDither(pJPEG, cx * mcuCX, mcuCY);
+                if ((x+1)*mcuCX > pJPEG->iWidth) { // right edge has clipped pixels
+                   jd.iWidthUsed = iPitch - (cx*mcuCX - pJPEG->iWidth);
+                }
                 if ((jd.y - pJPEG->iYOffset + mcuCY) > (pJPEG->iHeight>>iScaleShift)) { // last row needs to be trimmed
                    jd.iHeight = (pJPEG->iHeight>>iScaleShift) - (jd.y - pJPEG->iYOffset);
                 }
diff --git a/micropython/modules/jpegdec/jpegdec.cpp b/micropython/modules/jpegdec/jpegdec.cpp
index 57e9c59d..6153368e 100644
--- a/micropython/modules/jpegdec/jpegdec.cpp
+++ b/micropython/modules/jpegdec/jpegdec.cpp
@@ -95,6 +95,7 @@ MICROPY_EVENT_POLL_HOOK
         uint8_t *pixel = (uint8_t *)pDraw->pPixels;
         for(int y = 0; y < pDraw->iHeight; y++) {
             for(int x = 0; x < pDraw->iWidth; x++) {
+                if(x >= pDraw->iWidthUsed) break; // Clip to the used width
                 current_graphics->set_pen((uint8_t)(*pixel >> 4));
                 current_graphics->set_pixel({pDraw->x + x, pDraw->y + y});
                 pixel++;
@@ -104,6 +105,7 @@ MICROPY_EVENT_POLL_HOOK
         uint8_t *pixels = (uint8_t *)pDraw->pPixels;
         for(int y = 0; y < pDraw->iHeight; y++) {
             for(int x = 0; x < pDraw->iWidth; x++) {
+                if(x >= pDraw->iWidthUsed) break; // Clip to the used width
                 int i = y * pDraw->iWidth + x;
                 uint8_t p = pixels[i / 2];
                 p >>= (i & 0b1) ? 0 : 4;
@@ -116,6 +118,7 @@ MICROPY_EVENT_POLL_HOOK
         uint8_t *pixels = (uint8_t *)pDraw->pPixels;
         for(int y = 0; y < pDraw->iHeight; y++) {
             for(int x = 0; x < pDraw->iWidth; x++) {
+                if(x >= pDraw->iWidthUsed) break; // Clip to the used width
                 int i = y * pDraw->iWidth + x;
                 uint8_t p = pixels[i / 8];
                 p >>= 7 - (i & 0b111);
@@ -127,6 +130,7 @@ MICROPY_EVENT_POLL_HOOK
     } else {
         for(int y = 0; y < pDraw->iHeight; y++) {
             for(int x = 0; x < pDraw->iWidth; x++) {
+                if(x >= pDraw->iWidthUsed) break; // Clip to the used width
                 int i = y * pDraw->iWidth + x;
                 if (current_graphics->pen_type == PicoGraphics::PEN_RGB332) {
                     if (current_flags & FLAG_NO_DITHER) {