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Fix TFTDisplay::display to align pixels at 32-bit boundary (#9956)

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* Fix TFTDisplay partial update: align spans to 32-bit boundary for GDMA

The device, such as esp32c6, require 32-bit alignment for the data.

The patch aligns start and end of the update pixels buffer.

* Update src/graphics/TFTDisplay.cpp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Apply suggestion from @Copilot

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Ben Meadors <benmmeadors@gmail.com>
This commit is contained in:
notmasteryet
2026-04-02 20:57:19 -05:00
committed by GitHub
co-authored by GitHub Copilot Ben Meadors
parent efd2613bd7
commit e7ee4bea18
1 changed files with 15 additions and 7 deletions
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src/graphics/TFTDisplay.cpp
+15 -7
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@@ -1254,14 +1254,14 @@ void TFTDisplay::display(bool fromBlank)
// Did we find a pixel that needs updating on this row?
if (x_FirstPixelUpdate < displayWidth) {
// Align the first pixel for update to an even number so the total alignment of
// the data will be at 32-bit boundary, which is required by GDMA SPI transfers.
x_FirstPixelUpdate &= ~1;
// Quickly write out the first changed pixel (saves another array lookup)
linePixelBuffer[x_FirstPixelUpdate] = isset ? colorTftMesh : colorTftBlack;
x_LastPixelUpdate = x_FirstPixelUpdate;
// Step 3: copy all remaining pixels in this row into the pixel line buffer,
// while also recording the last pixel in the row that needs updating
for (x = x_FirstPixelUpdate + 1; x < displayWidth; x++) {
// Step 3a: copy rest of the pixels in this row into the pixel line buffer,
// while also recording the last pixel in the row that needs updating.
// Since the first changed pixel will be looked up, the x_LastPixelUpdate will be set.
for (x = x_FirstPixelUpdate; x < displayWidth; x++) {
isset = buffer[x + y_byteIndex] & y_byteMask;
linePixelBuffer[x] = isset ? colorTftMesh : colorTftBlack;
@@ -1274,6 +1274,14 @@ void TFTDisplay::display(bool fromBlank)
x_LastPixelUpdate = x;
}
}
// Step 3b: Round up the last pixel to odd number to maintain 32-bit alignment for SPIs.
// Most displays will have even number of pixels in a row -- this will be in bounds
// of the displayWidth. (Hopefully odd displays will just ignore that extra pixel.)
x_LastPixelUpdate |= 1;
// Ensure the last pixel index does not exceed the display width.
if (x_LastPixelUpdate >= displayWidth) {
x_LastPixelUpdate = displayWidth - 1;
}
#if defined(HACKADAY_COMMUNICATOR)
tft->draw16bitBeRGBBitmap(x_FirstPixelUpdate, y, &linePixelBuffer[x_FirstPixelUpdate],
(x_LastPixelUpdate - x_FirstPixelUpdate + 1), 1);