365 lines
12 KiB
C
365 lines
12 KiB
C
/*
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* Copyright (c) 2021 Arm Limited and Contributors. All rights reserved.
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* ST7796 TFT LCD Display Driver
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*
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* ==============================================================================
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* ABOUT THE ST7796 DISPLAY CONTROLLER
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* ==============================================================================
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*
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* The ST7796 is a single-chip controller/driver for 262K-color, graphic type
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* TFT-LCD displays. It consists of 960 source line and 480 gate line driving
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* circuits. This chip is capable of connecting directly to an external
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* microprocessor via an 8-bit/9-bit/16-bit/18-bit parallel interface or
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* Serial Peripheral Interface (SPI).
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*
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* Key Features:
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* - Resolution: Up to 480RGB x 320 dots
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* - Display Colors: 262K colors (RGB565 format - 16 bits per pixel)
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* - Interface: 4-wire SPI (used in this driver)
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* - Framebuffer: Internal RAM that holds the pixel data (480x320x16bit = 300KB)
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* - Power: 2.5V~3.3V I/O voltage, with internal regulators for LCD drivers
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*
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* ==============================================================================
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* SPI COMMUNICATION PROTOCOL
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* ==============================================================================
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*
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* The ST7796 uses a 4-wire SPI interface:
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* 1. SCK (Serial Clock) - Clock signal from MCU
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* 2. MOSI/SDA (Master Out Slave In) - Data signal from MCU to display
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* 3. CS (Chip Select) - Active LOW, selects the display
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* 4. DC (Data/Command) - HIGH for data, LOW for commands
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*
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* Additional pins:
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* 5. RST (Reset) - Hardware reset, active LOW
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* 6. BL (Backlight) - LED backlight control, HIGH for ON
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*
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* Communication sequence:
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* 1. Pull CS LOW to select the display
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* 2. Set DC LOW for command, HIGH for data
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* 3. Clock out 8 bits on MOSI while toggling SCK
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* 4. Pull CS HIGH to deselect
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*
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* ==============================================================================
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* RGB565 COLOR FORMAT
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* ==============================================================================
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*
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* RGB565 is a 16-bit color format:
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* - Red: 5 bits (bits 15-11) - 32 levels
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* - Green: 6 bits (bits 10-5) - 64 levels (human eye more sensitive to green)
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* - Blue: 5 bits (bits 4-0) - 32 levels
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*
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* Color encoding: RRRR RGGG GGGB BBBB
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* Example: 0xF800 = Red, 0x07E0 = Green, 0x001F = Blue, 0xFFFF = White
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*
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* ==============================================================================
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* DISPLAY ORIENTATION (MADCTL)
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* ==============================================================================
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*
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* MADCTL (0x36) controls memory access and display rotation:
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* - MY (bit 7): Row Address Order (flip vertical)
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* - MX (bit 6): Column Address Order (flip horizontal)
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* - MV (bit 5): Row/Column Exchange (swap X/Y for rotation)
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* - ML (bit 4): Vertical Refresh Order
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* - BGR (bit 3): RGB or BGR color order
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*
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* Current configuration: 0xE0 (MY=1, MX=1, MV=1)
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* This provides landscape mode (480x320) with correct orientation.
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*
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* ==============================================================================
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* MISSING FEATURES & POTENTIAL IMPROVEMENTS
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* ==============================================================================
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*
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* Currently NOT implemented (but supported by hardware):
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*
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* 1. HARDWARE SCROLLING:
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* - Vertical Scrolling Definition (VSCRDEF) and Vertical Scroll Start Address
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* - Could enable smooth scrolling without redrawing entire screen
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* - Useful for: text scrolling, game backgrounds, UI animations
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*
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* 2. PARTIAL DISPLAY MODE:
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* - Show only a portion of the display (save power)
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* - Commands: PTLON (0x12), PTLAR (0x30)
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*
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* 3. IDLE MODE:
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* - Reduced color depth (8 colors) for power saving
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* - Commands: IDMON (0x38), IDMOFF (0x39)
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*
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* 4. DISPLAY INVERSION:
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* - Currently set to INVOFF, but INVON available
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* - Some displays look better with inversion ON
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*
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* 5. TEAR EFFECT CONTROL:
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* - TE (Tearing Effect) pin synchronization
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* - Prevents tearing during screen updates
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* - Commands: TEON (0x35), TEOFF (0x34)
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*
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* 6. GAMMA CORRECTION:
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* - Fine-tune color accuracy and contrast
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* - Commands: PGC (0xE0), NGC (0xE1)
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*
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* 7. BRIGHTNESS/CONTRAST CONTROL:
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* - Software brightness via WRCABCMB command
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* - Currently only hardware backlight control
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*
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* 8. POWER CONTROL:
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* - Deep sleep modes
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* - Display ON/OFF without re-initialization
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* - Commands: SLPIN (0x10), SLPOUT (0x11)
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*
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* 9. DMA SUPPORT:
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* - Use DMA for SPI transfers instead of blocking writes
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* - Would significantly improve performance for large updates
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*
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* 10. DOUBLE BUFFERING:
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* - Currently single-buffered (direct to framebuffer)
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* - Could implement software double buffer for tear-free updates
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*
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* 11. IMAGE/BITMAP LOADING:
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* - Load images from SD card or flash
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* - BMP, PNG decoders
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*
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* 12. TEXT RENDERING:
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* - Font library for text display
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* - Variable font sizes
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*
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* 13. HARDWARE ACCELERATED FEATURES:
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* - Some displays have built-in shape drawing (not ST7796)
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* - Window clipping for faster partial updates
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*
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* Performance Optimization Ideas:
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* - Increase SPI speed beyond 80MHz (try 100-125MHz)
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* - Use DMA for background transfers
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* - Implement dirty rectangle tracking (only update changed areas)
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* - Cache frequently drawn graphics
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*
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* ==============================================================================
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*/
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#ifndef _PICO_ST7796_H_
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#define _PICO_ST7796_H_
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#include "hardware/spi.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* @brief Configuration structure for ST7796 display
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*
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* This structure holds all the pin mappings and SPI interface configuration
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* needed to communicate with the display. All GPIO pins should be valid
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* Raspberry Pi Pico pins, except gpio_cs which can be -1 to disable CS control.
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*/
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struct st7796_config {
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spi_inst_t* spi; // SPI instance (spi0 or spi1)
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uint gpio_din; // MOSI/SDA pin (data out from MCU)
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uint gpio_clk; // SCK pin (clock)
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int gpio_cs; // CS pin (chip select, -1 to disable)
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uint gpio_dc; // DC pin (data/command select)
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uint gpio_rst; // RST pin (hardware reset)
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uint gpio_bl; // Backlight pin (LED control)
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};
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/**
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* @brief Initialize the ST7796 display
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*
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* This function performs the complete initialization sequence:
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* 1. Configures all GPIO pins (SPI, CS, DC, RST, BL)
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* 2. Initializes SPI at 80-100 MHz
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* 3. Performs hardware reset
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* 4. Sends initialization commands to the display
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* 5. Sets up RGB565 color mode and landscape orientation
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* 6. Turns on backlight and display
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*
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* @param config Pointer to st7796_config structure with pin mappings
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* @param width Display width in pixels (typically 480 for landscape)
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* @param height Display height in pixels (typically 320 for landscape)
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*
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* Note: After this call, display is ready but blank. Call st7796_fill()
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* to clear with a color, or start drawing primitives.
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*/
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void st7796_init(const struct st7796_config *config, uint16_t width, uint16_t height);
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/**
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* @brief Fill entire display with a single color
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*
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* This is the fastest way to clear the screen or set a background.
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* Uses optimized 512-byte buffering for maximum SPI throughput.
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*
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* @param color RGB565 color value (e.g., 0x0000=black, 0xFFFF=white)
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*
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* Performance: ~15ms at 80MHz SPI for full 480x320 screen
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*/
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void st7796_fill(uint16_t color);
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/**
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* @brief Write a single pixel at current cursor position
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*
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* Writes one pixel without changing the drawing window. Use after
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* st7796_set_cursor() to position the write location. Rarely used
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* directly - most applications use st7796_draw_pixel() instead.
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*
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* @param color RGB565 color value
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*/
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void st7796_put(uint16_t color);
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/**
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* @brief Set cursor position for subsequent writes
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*
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* Sets the drawing window starting at (x, y) and extending to the
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* bottom-right of the display. Subsequent calls to st7796_put()
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* will write pixels starting from this position.
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*
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* @param x X coordinate (0 to width-1)
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* @param y Y coordinate (0 to height-1)
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*/
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void st7796_set_cursor(uint16_t x, uint16_t y);
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/**
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* @brief Write multiple pixels at current cursor position
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*
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* Writes an array of RGB565 color values starting at the current
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* cursor position. Advances the cursor automatically.
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*
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* @param data Pointer to array of RGB565 color values
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* @param len Number of pixels to write
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*
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* Note: Less efficient than fill_rect for solid colors due to
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* per-pixel conversion overhead.
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*/
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void st7796_write(const uint16_t *data, size_t len);
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/**
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* @brief Draw a single pixel at specified coordinates
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*
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* Draws one pixel at (x, y) with the specified color. This function
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* sets up a 1x1 drawing window, so it's slower than batch operations.
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* Use fill_rect() or other primitives when possible.
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*
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* @param x X coordinate (0 to width-1)
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* @param y Y coordinate (0 to height-1)
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* @param color RGB565 color value
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*
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* Performance: ~100-200 pixels/second due to window setup overhead
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*/
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void st7796_draw_pixel(uint16_t x, uint16_t y, uint16_t color);
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/**
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* @brief Draw a rectangle outline
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*
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* Draws a hollow rectangle with 1-pixel thick borders. Implemented
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* as 4 calls to fill_rect() for efficiency.
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*
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* @param x Top-left X coordinate
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* @param y Top-left Y coordinate
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* @param w Width in pixels
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* @param h Height in pixels
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* @param color RGB565 color value
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*/
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void st7796_draw_rect(uint16_t x, uint16_t y, uint16_t w, uint16_t h, uint16_t color);
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/**
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* @brief Draw a filled rectangle
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*
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* Draws a solid rectangle. This is one of the fastest drawing operations
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* due to optimized 512-byte buffering.
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*
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* @param x Top-left X coordinate
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* @param y Top-left Y coordinate
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* @param w Width in pixels
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* @param h Height in pixels
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* @param color RGB565 color value
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*
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* Performance: Can draw full screen in ~15ms at 80MHz SPI
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*/
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void st7796_fill_rect(uint16_t x, uint16_t y, uint16_t w, uint16_t h, uint16_t color);
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/**
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* @brief Draw a circle outline
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*
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* Draws a hollow circle using the midpoint circle algorithm (Bresenham).
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* Draws 8 symmetric points per iteration for efficiency.
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*
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* @param x0 Center X coordinate
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* @param y0 Center Y coordinate
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* @param r Radius in pixels
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* @param color RGB565 color value
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*
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* Note: Implemented as individual pixel draws, so performance is
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* O(r) with ~100-200 pixels/second throughput.
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*/
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void st7796_draw_circle(uint16_t x0, uint16_t y0, uint16_t r, uint16_t color);
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/**
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* @brief Draw a filled circle
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*
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* Draws a solid circle using midpoint circle algorithm with horizontal
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* line fills. Much faster than drawing individual pixels.
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*
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* @param x0 Center X coordinate
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* @param y0 Center Y coordinate
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* @param r Radius in pixels
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* @param color RGB565 color value
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*
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* Performance: Better than draw_circle due to fill_rect optimization
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*/
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void st7796_fill_circle(uint16_t x0, uint16_t y0, uint16_t r, uint16_t color);
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/**
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* @brief Draw a line between two points
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*
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* Draws a line using Bresenham's line algorithm. Works for any angle.
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*
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* @param x0 Start point X coordinate
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* @param y0 Start point Y coordinate
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* @param x1 End point X coordinate
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* @param y1 End point Y coordinate
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* @param color RGB565 color value
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*
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* Performance: O(max(dx, dy)) with ~100-200 pixels/second throughput
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*/
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void st7796_draw_line(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint16_t color);
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/**
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* @brief Draw a triangle outline
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*
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* Draws a hollow triangle by connecting three points with lines.
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*
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* @param x0 First vertex X coordinate
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* @param y0 First vertex Y coordinate
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* @param x1 Second vertex X coordinate
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* @param y1 Second vertex Y coordinate
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* @param x2 Third vertex X coordinate
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* @param y2 Third vertex Y coordinate
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* @param color RGB565 color value
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*/
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void st7796_draw_triangle(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint16_t x2, uint16_t y2, uint16_t color);
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/**
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* @brief Draw a filled triangle
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*
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* Draws a solid triangle using scanline fill algorithm. Sorts vertices
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* by Y coordinate and fills horizontal spans.
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*
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* @param x0 First vertex X coordinate
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* @param y0 First vertex Y coordinate
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* @param x1 Second vertex X coordinate
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* @param y1 Second vertex Y coordinate
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* @param x2 Third vertex X coordinate
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* @param y2 Third vertex Y coordinate
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* @param color RGB565 color value
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*
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* Performance: Better than draw_triangle due to fill_rect optimization
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*/
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void st7796_fill_triangle(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint16_t x2, uint16_t y2, uint16_t color);
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#ifdef __cplusplus
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}
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#endif
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#endif
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