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diff --git a/docs/quantum_painter_qgf.md b/docs/quantum_painter_qgf.md new file mode 100644 index 0000000000..caf6731e65 --- /dev/null +++ b/docs/quantum_painter_qgf.md @@ -0,0 +1,178 @@ +# QMK Graphics Format :id=qmk-graphics-format + +QMK uses a graphics format _("Quantum Graphics Format" - QGF)_ specifically for resource-constrained systems. + +This format is capable of encoding 1-, 2-, 4-, and 8-bit-per-pixel greyscale- and palette-based images. It also includes RLE for pixel data for some basic compression. + +All integer values are in little-endian format. + +The QGF is defined in terms of _blocks_ -- each _block_ contains a _header_ and an optional _blob_ of data. The _header_ contains the block's _typeid_, and the length of the _blob_ that follows. Each block type is denoted by a different _typeid_ has its own block definition below. All blocks are defined as packed structs, containing zero padding between fields. + +The general structure of the file is: + +* _Graphics descriptor block_ +* _Frame offset block_ +* Repeating list of frames: + * _Frame descriptor block_ + * _Frame palette block_ (optional, depending on frame format) + * _Frame delta block_ (optional, depending on delta flag) + * _Frame data block_ + +Different frames within the file should be considered "isolated" and may have their own image format and/or palette. + +## Block Header :id=qgf-block-header + +This block header is present for all blocks, including the graphics descriptor. + +_Block header_ format: + +```c +typedef struct __attribute__((packed)) qgf_block_header_v1_t { + uint8_t type_id; // See each respective block type + uint8_t neg_type_id; // Negated type ID, used for detecting parsing errors + uint24_t length; // 24-bit blob length, allowing for block sizes of a maximum of 16MB +} qgf_block_header_v1_t; +// _Static_assert(sizeof(qgf_block_header_v1_t) == 5, "qgf_block_header_v1_t must be 5 bytes in v1 of QGF"); +``` +The _length_ describes the number of octets in the data following the block header -- a block header may specify a _length_ of `0` if no blob is specified. + +## Graphics descriptor block :id=qgf-graphics-descriptor + +* _typeid_ = 0x00 +* _length_ = 18 + +This block must be located at the start of the file contents, and can exist a maximum of once in an entire QGF file. It is always followed by the _frame offset block_. + +_Block_ format: + +```c +typedef struct __attribute__((packed)) qgf_graphics_descriptor_v1_t { + qgf_block_header_v1_t header; // = { .type_id = 0x00, .neg_type_id = (~0x00), .length = 18 } + uint24_t magic; // constant, equal to 0x464751 ("QGF") + uint8_t qgf_version; // constant, equal to 0x01 + uint32_t total_file_size; // total size of the entire file, starting at offset zero + uint32_t neg_total_file_size; // negated value of total_file_size, used for detecting parsing errors + uint16_t image_width; // in pixels + uint16_t image_height; // in pixels + uint16_t frame_count; // minimum of 1 +} qgf_graphics_descriptor_v1_t; +// _Static_assert(sizeof(qgf_graphics_descriptor_v1_t) == (sizeof(qgf_block_header_v1_t) + 18), "qgf_graphics_descriptor_v1_t must be 23 bytes in v1 of QGF"); +``` + +## Frame offset block :id=qgf-frame-offset-descriptor + +* _typeid_ = 0x01 +* _length_ = variable + +This block denotes the offsets within the file to each frame's _frame descriptor block_, relative to the start of the file. The _frame offset block_ always immediately follows the _graphics descriptor block_. The contents of this block are an array of U32's, with one entry for each frame. + +Duplicate frame offsets in this block are allowed, if a certain frame is to be shown multiple times during animation. + +_Block_ format: + +```c +typedef struct __attribute__((packed)) qgf_frame_offsets_v1_t { + qgf_block_header_v1_t header; // = { .type_id = 0x01, .neg_type_id = (~0x01), .length = (N * sizeof(uint32_t)) } + uint32_t offset[N]; // where 'N' is the number of frames in the file +} qgf_frame_offsets_v1_t; +``` + +## Frame descriptor block :id=qgf-frame-descriptor + +* _typeid_ = 0x02 +* _length_ = 5 + +This block denotes the start of a frame. + +_Block_ format: + +```c +typedef struct __attribute__((packed)) qgf_frame_v1_t { + qgf_block_header_v1_t header; // = { .type_id = 0x02, .neg_type_id = (~0x02), .length = 5 } + uint8_t format; // Frame format, see below. + uint8_t flags; // Frame flags, see below. + uint8_t compression_scheme; // Compression scheme, see below. + uint8_t transparency_index; // palette index used for transparent pixels (not yet implemented) + uint16_t delay; // frame delay time for animations (in units of milliseconds) +} qgf_frame_v1_t; +// _Static_assert(sizeof(qgf_frame_v1_t) == (sizeof(qgf_block_header_v1_t) + 6), "qgf_frame_v1_t must be 11 bytes in v1 of QGF"); +``` + +If this frame is grayscale, the _frame descriptor block_ (or _frame delta block_ if flags denote a delta frame) is immediately followed by this frame's corresponding _frame data block_. + +If the frame uses an indexed palette, the _frame descriptor block_ (or _frame delta block_ if flags denote a delta frame) is immediately followed by this frame's corresponding _frame palette block_. + +Frame format possible values: + +* `0x00`: 1bpp grayscale, no palette, `0` = black, `1` = white, LSb first pixel +* `0x01`: 2bpp grayscale, no palette, `0` = black, `3` = white, linear interpolation of brightness, LSb first pixel +* `0x02`: 4bpp grayscale, no palette, `0` = black, `15` = white, linear interpolation of brightness, LSb first pixel +* `0x03`: 8bpp grayscale, no palette, `0` = black, `255` = white, linear interpolation of brightness, LSb first pixel +* `0x04`: 1bpp indexed palette, 2 colors, LSb first pixel +* `0x05`: 2bpp indexed palette, 4 colors, LSb first pixel +* `0x06`: 4bpp indexed palette, 16 colors, LSb first pixel +* `0x07`: 8bpp indexed palette, 256 colors, LSb first pixel + +Frame flags is a bitmask with the following format: + +| `bit 7` | `bit 6` | `bit 5` | `bit 4` | `bit 3` | `bit 2` | `bit 1` | `bit 0` | +|---------|---------|---------|---------|---------|---------|---------|--------------| +| - | - | - | - | - | - | Delta | Transparency | + +* `[1]` -- Delta: Signifies that the current frame is a delta frame, which specifies only a sub-image. The _frame delta block_ follows the _frame palette block_ if the image format specifies a palette, otherwise it directly follows the _frame descriptor block_. +* `[0]` -- Transparency: The transparent palette index in the _blob_ is considered valid and should be used when considering which pixels should be transparent during rendering this frame, if possible. + +Compression scheme possible values: + +* `0x00`: No compression +* `0x01`: [QMK RLE](quantum_painter_rle.md) + +## Frame palette block :id=qgf-frame-palette-descriptor + +* _typeid_ = 0x03 +* _length_ = variable + +This block describes the palette used for the frame. The _blob_ contains an array of palette entries -- one palette entry is present for each color used -- each palette entry is in QMK HSV888 format: + +```c +typedef struct __attribute__((packed)) qgf_palette_v1_t { + qgf_block_header_v1_t header; // = { .type_id = 0x03, .neg_type_id = (~0x03), .length = (N * 3 * sizeof(uint8_t)) } + struct { // container for a single HSV palette entry + uint8_t h; // hue component: `[0,360)` degrees is mapped to `[0,255]` uint8_t. + uint8_t s; // saturation component: `[0,1]` is mapped to `[0,255]` uint8_t. + uint8_t v; // value component: `[0,1]` is mapped to `[0,255]` uint8_t. + } hsv[N]; // N * hsv, where N is the number of palette entries depending on the frame format in the descriptor +} qgf_palette_v1_t; +``` + +## Frame delta block :id=qgf-frame-delta-descriptor + +* _typeid_ = 0x04 +* _length_ = 8 + +This block describes where the delta frame should be drawn, with respect to the top left location of the image. + +```c +typedef struct __attribute__((packed)) qgf_delta_v1_t { + qgf_block_header_v1_t header; // = { .type_id = 0x04, .neg_type_id = (~0x04), .length = 8 } + uint16_t left; // The left pixel location to draw the delta image + uint16_t top; // The top pixel location to draw the delta image + uint16_t right; // The right pixel location to to draw the delta image + uint16_t bottom; // The bottom pixel location to to draw the delta image +} qgf_delta_v1_t; +// _Static_assert(sizeof(qgf_delta_v1_t) == 13, "qgf_delta_v1_t must be 13 bytes in v1 of QGF"); +``` + +## Frame data block :id=qgf-frame-data-descriptor + +* _typeid_ = 0x05 +* _length_ = variable + +This block describes the data associated with the frame. The _blob_ contains an array of bytes containing the data corresponding to the frame's image format: + +```c +typedef struct __attribute__((packed)) qgf_data_v1_t { + qgf_block_header_v1_t header; // = { .type_id = 0x05, .neg_type_id = (~0x05), .length = N } + uint8_t data[N]; // N data octets +} qgf_data_v1_t; +``` |