Panel_M5UnitLCD: fix ARGB image writes, reads after image writes and the first draw after reset

[ainyan03]

What changes

writeImageARGB drew only one row. It set a one-row window and sent the first w pixels of src_data, ignoring h and the source position. pushAlphaImage() passes the whole clipped rectangle, so only the first row appeared, and with clipping on the left or top the wrong pixels were sent. Rows are now sent in a window of h rows, each pixel indexed through src_x32 / src_y32 / src_bitwidth as the pixel copy functions do.

bgra8888_t images came out in the wrong colors. pushAlphaImage() accepts both argb8888_t and bgra8888_t, and every source pixel was byte-swapped as if it were argb8888_t. Sources tagged argb8888_4Byte (bgra8888_t) are now sent without the swap; every other source, including the one-row buffer of the anti-aliased rotate/zoom path, is sent as before.

Image data lost right after init(). After CMD_RESET the unit answers READ_ID and consumes a NOP at once, but its first drawing command takes about 250 ms more, and pixel data streamed in that period is dropped. An image drawn right after init() lost its rows after the first dozen (both raw ARGB and RLE images); short fill commands were not affected. The reset path now queues a one-pixel fill and waits, with the same buffer-count wait readRect() uses, until the unit has consumed it. init() with reset takes about 250 ms longer; init_without_reset() is unchanged.

readRect() returned zeros right after an image write. When the read used the same column range as the cached window, _set_window() skipped CASET, and the unit then answered the read with zeros. Reading a full-width row right after a full-width pushImage() or pushAlphaImage() therefore gave all zeros. readRect() now always sends the window; this costs a few bytes per read.

Checked

• Hardware: Unit LCD on a DinMeter (ESP32-S3) Port B, 400 kHz unless noted. Images are opaque gradients, read back with readPixel() unless noted.

Case	Before	After
pushAlphaImage (argb8888_t) 40x30 at (10,10)	1160 / 1200 pixels wrong (only row 0 drawn)	0 / 1200
pushAlphaImage 40x30 at (-10,-8) (clipped left and top)	660 / 660 wrong	0 / 660
pushAlphaImage (bgra8888_t) 40x30	1200 / 1200 wrong colors	0 / 1200
pushImage (RGB565) 40x30 drawn right after init()	713 / 1200 wrong (rows from 12 missing)	0 / 1200
full-width image (RGB565 or ARGB), then readRect() of full-width rows	read as all zeros	0 / 32400 (135x240)
pushAlphaImage 135x240 in one call at 1 MHz	—	0 / 32400

• Builds with Arduino 2.0.x (ESP-IDF 4.4) / 3.x and ESP-IDF 5.1 to 6.1 across ESP32, S3, C3, C5, C6, C61, H2 and P4.