rp_pico_display_engine/README.md

RP Pico Display Engine

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

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

Quick Start

1. Add as a subproject (recommended)

The most practical integration pattern is to add this repository (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.

cmake_minimum_required(VERSION 3.18.4)
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
    # Uncomment if/when you need these primitives:
    # ${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
)

target_compile_definitions(display_engine PUBLIC
    DISPLAY_TYPE=DISPLAY_TYPE_ST7789
    DISPLAY_SPI_PORT=spi1
    DISPLAY_PIN_MOSI=15
    DISPLAY_PIN_SCK=14
    DISPLAY_PIN_CS=13
    DISPLAY_PIN_DC=12
    DISPLAY_PIN_RST=11
    DISPLAY_PIN_BL=10
)

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

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, defaults from src/core/display_driver.h are used.

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)

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

Display config is set in Examples/Thermometr/CMakeLists.txt via target_compile_definitions(...): DISPLAY_TYPE, DISPLAY_SPI_PORT, DISPLAY_PIN_MOSI, DISPLAY_PIN_SCK, DISPLAY_PIN_CS, DISPLAY_PIN_DC, DISPLAY_PIN_RST, DISPLAY_PIN_BL.

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: SCENARIOS.ru.md.