rp_pico_display_engine/README.md

RP Pico Display Engine

A lightweight C display engine for RP2040/RP2350 and ST7789 / ILI9341 SPI displays (DMA) with an explicit begin/end paint frame contract.

https://github.com/user-attachments/assets/0de36c89-4f57-4a90-a6db-7a84c19ec3cc

Features

• Two modes: DISPLAY_MODE_SAFE and DISPLAY_MODE_RAW
• 1 or 2 frame buffers (buffer_count)
• Non-blocking and blocking frame acquisition:
  • display_begin_paint_try()
  • display_begin_paint_blocking()
• Safe frame completion via display_end_paint()
• Rendering primitives and a font module with Cyrillic support

Repository Structure

• include/display/ - public headers for the engine and renderer
• src/core/display.c - display engine core
• src/render/ - primitives implementation
• include/Font/, src/Font/ - font data and text rendering
• Examples/Thermometr/ - working Pico SDK example project

Required Environment

• git
• cmake version 3.18.4+
• build tool supported by CMake (make by default on Unix-like systems)
• Pico SDK with PICO_SDK_PATH pointing to it
• ARM toolchain arm-none-eabi-gcc

Supported Displays and Default Wiring

Supported controller backends:

• DISPLAY_TYPE_ST7789
• DISPLAY_TYPE_ILI9341

If you do not pass any display-related compile definitions, the library defaults from src/core/display_driver.h are used:

• Controller: DISPLAY_TYPE_ST7789
• SPI port: spi0
• MOSI=19
• SCK=18
• CS=17
• DC=22
• RST=13
• BL=12

These defaults mean: if you build without overriding pins or DISPLAY_TYPE, the firmware is meant for an ST7789 display wired to those RP2040/RP2350 GPIOs.

Quick Start

1. Add as vendored sources via git submodule (recommended)

The most practical integration pattern is to add this repository as a vendored dependency (for example, as a git submodule) and build display_engine from your main CMakeLists.txt. You do not have to include all rendering primitives immediately: keep only what you need and uncomment extra modules later.

Create a new project and add this repository as a submodule:

mkdir pico_display_app
cd pico_display_app
git init
git submodule add https://github.com/stasenso/rp_pico_display_engine.git external/rp_pico_display_engine
git submodule update --init --recursive
mkdir -p src

Make sure PICO_SDK_PATH is set:

export PICO_SDK_PATH=/absolute/path/to/pico-sdk

Create the root CMakeLists.txt:

cat > CMakeLists.txt <<'EOF'
cmake_minimum_required(VERSION 3.18.4)

# EN: Change to `pico` for RP2040-based boards or keep `pico2` for Pico 2 / RP2350.
# RU: Замените на `pico` для плат на RP2040 или оставьте `pico2` для Pico 2 / RP2350.
set(PICO_BOARD pico2 CACHE STRING "Pico SDK target board")

include($ENV{PICO_SDK_PATH}/external/pico_sdk_import.cmake)

project(my_app C CXX ASM)
set(CMAKE_C_STANDARD 11)
set(CMAKE_CXX_STANDARD 17)

pico_sdk_init()

set(DISPLAY_ENGINE_DIR ${CMAKE_CURRENT_LIST_DIR}/external/rp_pico_display_engine)

add_library(display_engine STATIC
    ${DISPLAY_ENGINE_DIR}/src/Font/font_data.c
    ${DISPLAY_ENGINE_DIR}/src/core/display.c
    ${DISPLAY_ENGINE_DIR}/src/core/display_transport.c
    ${DISPLAY_ENGINE_DIR}/src/core/display_driver.c
    ${DISPLAY_ENGINE_DIR}/src/render/context.c
    ${DISPLAY_ENGINE_DIR}/src/render/line.c
    # EN: Uncomment these sources if/when you need the extra primitives.
    # RU: Раскомментируйте эти исходники, если понадобятся дополнительные примитивы.
    # ${DISPLAY_ENGINE_DIR}/src/render/grid.c
    # ${DISPLAY_ENGINE_DIR}/src/render/sine_wave.c
    # ${DISPLAY_ENGINE_DIR}/src/render/bezier.c
)

target_include_directories(display_engine PUBLIC
    ${DISPLAY_ENGINE_DIR}/include
    ${DISPLAY_ENGINE_DIR}/include/display
)

target_link_libraries(display_engine PUBLIC
    pico_stdlib
    hardware_spi
    hardware_dma
    hardware_timer
    pico_multicore
)

# EN: Change the SPI bus, GPIO pins, and display controller here to match your wiring.
# RU: Здесь измените SPI-шину, GPIO-пины и контроллер дисплея под вашу схему подключения.
target_compile_definitions(display_engine PUBLIC
    # EN: Select the display controller backend: ST7789 or ILI9341.
    # RU: Выберите бэкенд контроллера дисплея: ST7789 или ILI9341.
    DISPLAY_TYPE=DISPLAY_TYPE_ST7789
    # EN: Select the SPI peripheral connected to the display: spi0 or spi1.
    # RU: Выберите SPI-периферию, к которой подключён дисплей: spi0 или spi1.
    DISPLAY_SPI_PORT=spi1
    DISPLAY_PIN_MOSI=15  # DIN / SDA
    DISPLAY_PIN_SCK=14   # CLK / SCL / SCK
    DISPLAY_PIN_CS=13    # CS / SS
    DISPLAY_PIN_DC=12    # DC / A0 / RS
    DISPLAY_PIN_RST=11   # RST / RES / RESET
    DISPLAY_PIN_BL=10    # BL / LED / LEDK
)

add_executable(my_app src/main.c)
target_link_libraries(my_app PRIVATE display_engine)
pico_add_extra_outputs(my_app)
EOF

Create src/main.c:

cat > src/main.c <<'EOF'
#include "pico/stdlib.h"
#include "display/display.h"
#include "display/render/context.h"

int main(void) {
    stdio_init_all();

    display_config_t cfg = {
        .width = 320,
        .height = 240,
        .buffer_count = 1,
        .mode = DISPLAY_MODE_SAFE
    };
    display_init(&cfg);

    render_ctx_t rc;

    while (1) {
        uint16_t *buf = display_begin_paint_blocking();
        render_begin(&rc, buf, 320, 240);
        render_clear(&rc, RGB16(0, 0, 0));
        display_end_paint();
        sleep_ms(16);
    }
}
EOF

Build the project:

cmake -S . -B build
cmake --build build

2. Change display pins and controller type

Set these compile definitions on display_engine:

• DISPLAY_SPI_PORT (spi0 or spi1)
• DISPLAY_PIN_MOSI, DISPLAY_PIN_SCK, DISPLAY_PIN_CS, DISPLAY_PIN_DC, DISPLAY_PIN_RST, DISPLAY_PIN_BL
• DISPLAY_TYPE (DISPLAY_TYPE_ST7789 or DISPLAY_TYPE_ILI9341)

If no definitions are provided, these defaults from src/core/display_driver.h are used:

• DISPLAY_TYPE=DISPLAY_TYPE_ST7789
• DISPLAY_SPI_PORT=spi0
• DISPLAY_PIN_MOSI=19
• DISPLAY_PIN_SCK=18
• DISPLAY_PIN_CS=17
• DISPLAY_PIN_DC=22
• DISPLAY_PIN_RST=13
• DISPLAY_PIN_BL=12

3. Safe mode with a single display loop

Good for a simple loop where dropping a frame is acceptable when the buffer is busy.

#include "display/display.h"
#include "display/render/context.h"

#define WIDTH  320
#define HEIGHT 240

void app_loop(void) {
    display_config_t cfg = {
        .width = WIDTH,
        .height = HEIGHT,
        .buffer_count = 1,
        .mode = DISPLAY_MODE_SAFE
    };
    display_init(&cfg);

    render_ctx_t rc;

    while (1) {
        uint16_t *buf = display_begin_paint_try();
        if (!buf) {
            continue;
        }

        render_begin(&rc, buf, WIDTH, HEIGHT);
        render_clear(&rc, RGB16(0, 0, 0));
        // draw...

        bool ok = display_end_paint();
        hard_assert(ok);
    }
}

4. Safe mode with two buffers and deferred submit support

In SAFE + buffer_count = 2, DMA can scan out one buffer while you render the other one.
If DMA is busy at display_end_paint(), the frame may be deferred (single pending-frame queue).

#include "display/display.h"
#include "display/render/context.h"

#define WIDTH  320
#define HEIGHT 240

void app_loop(void) {
    display_config_t cfg = {
        .width = WIDTH,
        .height = HEIGHT,
        .buffer_count = 2,
        .mode = DISPLAY_MODE_SAFE
    };
    display_init(&cfg);

    render_ctx_t rc;

    while (1) {
        uint16_t *buf = display_begin_paint_try();
        if (!buf) {
            // DMA/queue busy: run other app logic
            continue;
        }

        render_begin(&rc, buf, WIDTH, HEIGHT);
        render_clear(&rc, RGB16(8, 16, 8));
        // draw...

        bool accepted = display_end_paint();
        hard_assert(accepted); // false only on contract misuse
    }
}

5. Primitive and font headers + output example

Minimal include set:

#include "display/display.h"
#include "display/render/context.h"
#include "display/render/line.h"
#include "Font/font_data.h"            // draw_string(), draw_char(), get_char_width()

Optional includes (uncomment when needed):

// #include "display/render/grid.h"
// #include "display/render/sine_wave.h"
// #include "display/render/bezier.h"

Primitive + text render example:

render_ctx_t rc;
render_begin(&rc, buf, 320, 240);

render_clear(&rc, RGB16(9, 19, 9));
render_line(&rc, 0, 0, 319, 239, RGB16(255, 0, 0));
// render_grid(&rc, 20, 20, 40, RGB16(12, 26, 13)); // uncomment if you need grid
// render_sine_wave(&rc, 960, 100, 2.0f, 0, 120, phase, RGB16(0, 255, 0)); // uncomment if needed

int px[4] = {20, 80, 140, 220};
int py[4] = {200, 120, 220, 160};
// render_bezier(&rc, px, py, 4, RGB16(255, 255, 0)); // uncomment if needed

draw_string(&rc, 16, 16, L"Cyrillic check", RGB565(255, 255, 255));

Build Example (Pico SDK)

If you just want to build the ready-made example from this repository:

cd Examples/Thermometr
mkdir -p build && cd build
cmake ..
cmake --build .

This example sets the target board directly in Examples/Thermometr/CMakeLists.txt. To switch boards, change:

set(PICO_BOARD pico2 CACHE STRING "Pico SDK target board")

Use pico for RP2040-based Pico or pico2 for RP2350-based Pico 2. The display configuration in the same file is:

• Controller: DISPLAY_TYPE_ILI9341
• SPI port: spi1
• MOSI=15
• SCK=14
• CS=13
• DC=12
• RST=11
• BL=10

There is also Examples/EngineDemo/CMakeLists.txt, which defaults to:

• Board: Pico 2 / RP2350 (PICO_BOARD=pico2)
• Controller: DISPLAY_TYPE_ST7789
• SPI port: spi1
• MOSI=15
• SCK=14
• CS=13
• DC=12
• RST=11
• BL=10

So the produced .uf2 must be flashed to the board selected by that example's CMake config, and the display must be wired to the pins listed there.

API Contract (Important)

• Every successful display_begin_paint_*() must be followed by display_end_paint()
• Do not call a second begin until the current paint section is closed
• Do not call display_submit() manually inside an open paint section

Detailed usage scenarios are documented in Russian in SCENARIOS.ru.md.