gint/include/gint/image.h

//---
// gint:image - Image manipulation and rendering
//
// Note: this module is currently only available on fx-CG.
//
// This header provides image manipulation functions. This mainly consists of a
// reference-based image format, various access and modification functions, and
// a number of high-performance transformations and rendering effects. If you
// find yourself limited by rendering time, note that RAM writing speed is
// often the bottleneck, and image rendering is much faster in Azur (which is
// what the renderer was initially designed for).
//
// This module supports 3 bit depths: full-color 16-bit (RGB565), indexed 8-bit
// (P8) and indexed 4-bit (P4). All three have an "alpha" variation where one
// color is  treated as transparent, leading to 6 total formats.
//
// The image renderers support so-called *dynamic effects*, which are image
// transformations performed on-the-fly while rendering, without generating an
// intermediate image. They comprise straightforward transformations that
// achieve similar performance to straight rendering and can be combined to
// some extent, which makes them reliable whenever applicable.
//
// For images of the RGB16 and P8 bit depths, the module supports a rich API
// with image subsurfaces and a fairly large sets of geometric and color
// transforms, including some in-place. P4 is not supported in most of these
// functions because the dense bit packing is both impractical and slower for
// these applications.
//---

#ifndef GINT_IMAGE
#define GINT_IMAGE

#ifdef __cplusplus
extern "C" {
#endif

#ifndef FXCG50
#error <gint/image.h> is only supported on FXCG50
#else

#include <gint/defs/attributes.h>
#include <gint/defs/types.h>

//---
// Image structures
//---

/* Image formats. Note that transparency really only indicates the default
   rendering method, as a transparent background can always be added or removed
   by a dynamic effect on any image. */
enum {
    IMAGE_RGB565      = 0,  /* RGB565 without alpha */
    IMAGE_RGB565A     = 1,  /* RGB565 with one transparent color */
    IMAGE_P8_RGB565   = 4,  /* 8-bit palette, all opaque colors */
    IMAGE_P8_RGB565A  = 5,  /* 8-bit with one transparent color */
    IMAGE_P4_RGB565   = 6,  /* 4-bit palette, all opaque colors */
    IMAGE_P4_RGB565A  = 3,  /* 4-bit with one transparent color */

    IMAGE_DEPRECATED_P8 = 2,
};

/* Quick macros to compare formats by storage size */
#define IMAGE_IS_RGB16(format) \
    ((format) == IMAGE_RGB565 || (format) == IMAGE_RGB565A)
#define IMAGE_IS_P8(format) \
    ((format) == IMAGE_P8_RGB565 || (format) == IMAGE_P8_RGB565A)
#define IMAGE_IS_P4(format) \
    ((format) == IMAGE_P4_RGB565 || (format) == IMAGE_P4_RGB565A)
/* Check whether image format has an alpha color */
#define IMAGE_IS_ALPHA(format) \
    ((format) == IMAGE_RGB565A || \
     (format) == IMAGE_P8_RGB565A || \
     (format) == IMAGE_P4_RGB565A)
/* Check whether image format uses a palette */
#define IMAGE_IS_INDEXED(format) \
    (IMAGE_IS_P8(format) || IMAGE_IS_P4(format))

/* Image flags. These are used for memory management, mostly. */
enum {
    IMAGE_FLAGS_DATA_RO         = 0x01,  /* Data is read-only */
    IMAGE_FLAGS_PALETTE_RO      = 0x02,  /* Palette is read-only */
    IMAGE_FLAGS_DATA_ALLOC      = 0x04,  /* Data is malloc()'d */
    IMAGE_FLAGS_PALETTE_ALLOC   = 0x08,  /* Palette is malloc()'d */
};

/* image_t: gint's native bitmap image format
   Images of this format can be created through this header's API but also by
   using the fxSDK's built-in image converters with fxconv. */
typedef struct
{
    /* Color format, one of the IMAGE_* values defined above */
    uint8_t format;
    /* Additional flags, a combination of IMAGE_FLAGS_* values */
    uint8_t flags;
    /* For formats with alpha, value or index used for transparency */
    uint16_t alpha;
    /* Full width and height, in pixels */
    uint16_t width;
    uint16_t height;
    /* Byte stride between lines */
    int stride;

    /* Pixel data in row-major order, left to right.

       RGB16:
       - 2 bytes per entry, each row padded to 4 bytes for alignment
       - Each 2-byte value is an RGB565 color
       P8:
       - 1 byte per entry
       - Each byte is a shifted palette index (to access the palette, use:
         palette.colors[<value>+128])
       P4:
       - 4 bits per entry, each row padded to a full byte
       - Each entry is a palette index (0...15) */
    void *data;

    /* For P8 and P4, palette. The color count does not account for alpha
       (which is usually the last entry, but not materialized) and instead
       indicates how much memory is allocated. */
    int color_count;
    uint16_t *palette;

} GPACKED(4) image_t;

/* Dynamic effects: these transformations can be applied on images while
   rendering. Not all effects can be combined; unless specified otherwise:
   - HFLIP and VFLIP can both be added regardless of any other effect
   - At most one color effect can be applied */
enum {
    /* Value 0x01 is reserved, because it is DIMAGE_NOCLIP, which although
       part of the old API still needs to be supported. */

    /* [Any]: Skip clipping the command against the source image */
    IMAGE_NOCLIP_INPUT   = 0x04,
    /* [Any]: Skip clipping the command against the output VRAM */
    IMAGE_NOCLIP_OUTPUT  = 0x08,
    /* [Any]: Skip clipping both */
    IMAGE_NOCLIP         = IMAGE_NOCLIP_INPUT | IMAGE_NOCLIP_OUTPUT,

    // Geometric effects. These values should remain at exactly bit 8 and
    // following, or change gint_image_mkcmd() along with it.

    /* [Any]: Flip image vertically */
    IMAGE_VFLIP          = 0x0100,
    /* [Any]: Flip image horizontally */
    IMAGE_HFLIP          = 0x0200,

    // Color effects

    /* [RGB565, P8_RGB565, P4_RGB565]: Make a color transparent
       Adds one argument:
       * Color to clear (RGB16: 16-bit value; P8/P4: palette index) */
    IMAGE_CLEARBG        = 0x10,
    /* [RGB565, P8_RGB565, P4_RGB565]: Turn a color into another
       Adds two arguments:
       * Color to replace (RGB16: 16-bit value; P8/P4: palette index)
       * Replacement color (16-bit value) */
    IMAGE_SWAPCOLOR      = 0x20,
    /* [RGB565A, P8_RGB565A, P4_RGB565A]: Add a background
        Adds one argument:
        * Background color (16-bit value) */
    IMAGE_ADDBG          = 0x40,
    /* [RGB565A, P8_RGB565A, P4_RGB565A]: Dye all non-transparent pixels
       Adds one argument:
       * Dye color (16-bit value) */
    IMAGE_DYE            = 0x80,
};

//---
// Image creation and destruction
//---

/* image_alloc(): Create a new (uninitialized) image

   This function allocates a new image of the specified dimensions and format.
   It always allocates a new data array, though a palette from another image
   can be reused. (If you need to reuse a data array, see image_create() below
   or use img_create_sub().)

   The first parameters [width] and [height] specify the dimensions of the new
   image in pixels. The [format] should be one of the IMAGE_* formats, for
   example IMAGE_RGB565A or IMAGE_P4_RGB565.

   By default, a new palette is allocated for formats with palettes; the new
   image owns the palette and frees it when freed. This can be overriden by
   setting the [palette] pointer to the desired palette; in this case, the new
   image does not own the palette and does not free it when freed.

   Regardless of whether the palette is allocated or specified by hand, for P8
   the palette size must be indicated. A value of -1 can be specified to use
   the default (256 colors). For all other formats, set a value of -1.

   For images with alpha, the last parameter [alpha] indicates the palette
   index or color value that denotes transparent pixels.

   The returned image structure must be freed with image_free() after use.

   @width         Width of the new image
   @height        Height of the new image
   @format        Pixel format; one of the IMAGE_* formats defined above
   @palette       If not NULL, specifies the palette instead of allocating it
   @palette_size  For P8, indicates the palette size to use
   @alpha         For formats with alpha, color or index denoting alpha */
image_t *image_alloc(int width, int height, int format,
    void *palette, int palette_size, int alpha);

/* image_create(): Create a bare image with no data/palette

   This function allocates a new image structure but without data or palette.
   The [data] and [palette] members are NULL, and [color_count] is either 0 or
   -1 depending on whether the format normally has a palette.

   This function is useful to create images that reuse externally-provided
   information. It is intended that the user of this function sets the [data],
   [stride] and [palette] and [color_count] members themselves. The
   IMAGE_FLAGS_DATA_ALLOC and the IMAGE_FLAGS_PALETTE_ALLOC flags can be set on
   the image if the user wishes for the image to free its data and palette when
   freed.

   For images with alpha, the last parameter [alpha] indicates the palette
   index or color value that denotes transparent pixels.

   The returned image structure must be freed with image_free() after use. */
image_t *image_create(int width, int height, int format, int alpha);

/* image_create_vram(): Create a reference to gint_vram

   This function creates a new RGB565 image that references gint_vram. Using
   this image as target for transformation functions can effectively render
   transformed images to VRAM.

   The value of gint_vram is captured when this function is called, and does
   not update after dupdate() when triple-buffering is used. The user should
   account for this option. (Using this function twice then replacing one of
   the [data] pointers is allowed.)

   The VRAM image ows no data but it does own its own structure so it must
   still be freed with image_free() after use. */
image_t *image_create_vram(void);

/* image_free(): Free and image and the data it owns

   This function frees the provided image structure and the data that it owns.
   Images converted by fxconv should not be freed; nonetheless, this functions
   distinguishes them and should work. Images are not expected to be created on
   the stack.

   If the image has the IMAGE_FLAGS_DATA_ALLOC flag, the data pointer is also
   freed. Similarly, the image has the IMAGE_FLAGS_PALETTE_ALLOC flag, the
   palette is freed. Make sure to not free images when references to them still
   exist, as this could cause the reference's pointers to become dangling. */
void image_free(image_t *img);

/* image_copy_palette(): Duplicate an image's palette

   This function duplicates the palette and returns a new one allocated with
   malloc(). If the input image is not in a palette format or has no palette
   assigned, returns NULL. If the returned pointer is not NULL, free() after
   use or set the IMAGE_FLAGS_PALETTE_ALLOC flag on the image holding it so
   that free() is automatically called when the image is freed. */
uint16_t *image_copy_palette(image_t const *img);

//---
// Basic image access and information
//---

/* image_valid(): Check if an image is valid
   An image is considered valid if it has a valid profile, a non-NULL data
   pointer, and for palette formats a valid palette pointer. */
bool image_valid(image_t const *img);

/* image_get_pixel(): Read a pixel from the data array

   This function reads a pixel from the image's data array at position (x,y).
   It returns the pixel's value, which is either a full-color value (RGB16) or
   a possibly-negative palette index (P8/P4). See the description of the [data]
   field of image_t for more details. The value of the pixel can be decoded
   into a 16-bit color either manually or by using the image_decode_pixel()
   function.

   Note that reading large amounts of image data with this function will be
   slow; if you need reasonable performance, consider iterating on the data
   array manually. */
int image_get_pixel(image_t const *img, int x, int y);

/* image_decode_pixel(): Decode a pixel value

   This function decodes a pixel's value obtained from the data array (for
   instance with image_get_pixel()). For RGB16 formats this does nothing, but
   for palette formats this accesses the palette at a suitable position.

   Note that reading large amounts of data with this function will be slow; if
   you need reasonable performance, consider inlining the format-specific
   method or iterating on the data array manually. */
int image_decode_pixel(image_t const *img, int pixel);

/* image_data_size(): Compute the size of the [data] array
   This function returns the size of the data array, in bytes. This can be used
   to duplicate it. Note that for sub-images this is a subsection of another
   image's data array, and might be much larger than the sub-image. */
int image_data_size(image_t const *img);

/* image_palette_size(): Compute the size of the [palette] array
   This function returns the size of the palette array, in bytes. This can be
   used to duplicate the palette. For images without a palette, returns -1. */
int image_palette_size(image_t const *img);

//---
// Basic image modifications
//---

/* image_set_pixel(): Set a pixel in the data array

   This function writes a pixel into the image's data array at position (x,y).
   The pixel value must be of the proper format, as specified in the definition
   of the [data] field of image_t.

   Formats: RGB16, P8, P4 */
void image_set_pixel(image_t const *img, int x, int y, int value);

/* image_copy(): Copy an image into another one

   This function copies an image into another image. The target must be a valid
   image with the same format as the source, otherwise this function is a
   no-op. Unlike transforms, this function does clip, so there are no
   conditions on the size of the target.

   If [copy_alpha] is true, transparent pixels are copied verbatim, which
   effectively replaces the top-left corner of [dst] with [src]. If it's false,
   transparent pixels of [src] are skipped, effectively rendering [src] over
   the top-left corner of [src].

   The color scheme of src and dst should normally match. In RGB16, if
   src->alpha and dst->alpha differ, this function adopts a resonable behavior;
   inputs of value src->alpha are turned into dst->alpha if copy_alpha is true,
   ignored otherwise; and opaque inputs of value dst->alpha are turned into
   [dst->alpha ^ 1] to keep the visuals consistent. In P8, no attempt is made
   to merge the palettes.

   Formats: RGB16, P8 */
void image_copy(image_t const *src, image_t *dst, bool copy_alpha);

/* image_fill(): Fill an image with a single pixel value */
void image_fill(image_t *img, int value);

/* image_clear(): Fill a transparent image with its transparent value */
void image_clear(image_t *img);

/* TODO: Expand by taking from libimg */

//---
// Sub-image extraction
//---

/* image_sub(): Build a reference to a sub-image

   This function is used to create references to sub-images of RGB16 and P8
   images. The [data] pointer of the sub-image points somewhere within the data
   array of the source, and its [palette] pointer is identical to the source's.

   The last parameter is a pointer to a preallocated image_t structure (usually
   on the stack) that gets filled with the data. Doing this instead of
   allocating a new object with malloc() means that there is no need to
   image_free() the sub-image, and thus it can be used inline:

     image_t tmp;
     image_hflip(src, image_sub(dst, x, y, w, h, &tmp));

   A preprocessor macro is used to make the last parameter optional. If it's
   not specified, a pointer to a static image_t will be returned instead. This
   is useful in inline calls as shown above, which then simplify to:

     image_hflip(src, image_sub(dst, x, y, w, h));

   However, another call to image_sub() or image_at() will override the
   sub-image, so you should only use this in such temporary settings.

   If the requested rectangle does not intersect the source, the sub-image will
   be of dimension 0x0. If the image format does not support sub-images (P4),
   the sub-image will test invalid with image_valid(). */
image_t *image_sub(image_t const *src, int x, int y, int w, int h,
    image_t *dst);

/* Make the last parameter optional */
#define image_sub1(src, x, y, w, h, dst, ...) image_sub(src, x, y, w, h, dst)
#define image_sub(...) image_sub(__VA_ARGS__, NULL)

/* image_at(): Build a reference to a position within a sub-image */
#define image_at(img, x, y) image_sub(img, x, y, -1, -1)

//---
// Geometric image transforms
//---

/* TODO: Geometric transforms */

//---
// Color transforms
//---

/* TODO: Color transforms */

//---
// Image rendering functions
//
// The following functions extend dimage() and dsubimage(). The [effects]
// parameter takes a combination of IMAGE_* flags and effects, limited to the
// combinations previously described, with additional arguments depending on
// the color effect being applied.
//
//   dimage_effect(x, y, img, effects, ...)
//   dsubimage_effect(x, y, img, left, top, w, h, effects, ...)
//
// However if you use these super-generic functions you will link the code for
// all effects and all formats into your add-in, which takes a fair amount of
// space. If that's a problem, you can use the more specific functions below:
//
// * dimage_<FORMAT>_<EFFECT>() for one particular format (rgb16, p8, p4) along
//   with one particular color effect (clearbg, swapcolor, addbg, dye).
// * dimage_<FORMAT>() is like the above when no color effect is applied.
//
// All of them support the HFLIP and VFLIP flags. For effect-specific functions
// the corresponding effect flag can be omitted (fi. IMAGE_CLEARBG is implicit
// when using dimage_p8_clearbg()).
//---

/* dimage_effect(): Generalized dimage() supporting dynamic effects */
#define dimage_effect(x, y, img, eff, ...) \
    dsubimage_effect(x, y, img, 0, 0, (img)->width, (img)->height, eff, \
        ##__VA_ARGS__)
/* dsubimage_effect(): Generalized dsubimage() supporting dynamic effects */
void dsubimage_effect(int x, int y, image_t const *img,
    int left, int top, int w, int h, int effects, ...);

/* Specific versions for each format */
#define DIMAGE_SIG1(NAME, ...) \
    void dimage_ ## NAME(int x, int y, image_t const *img,##__VA_ARGS__); \
    void dsubimage_ ## NAME(int x, int y, image_t const *img, \
        int left, int top, int w, int h, ##__VA_ARGS__);
#define DIMAGE_SIG(NAME, ...) \
    DIMAGE_SIG1(rgb16 ## NAME, ##__VA_ARGS__) \
    DIMAGE_SIG1(p8 ## NAME, ##__VA_ARGS__) \
    DIMAGE_SIG1(p4 ## NAME, ##__VA_ARGS__)

/* d[sub]image_{rgb16,p8,p4}_effect(..., effects, <extra arguments>) */
DIMAGE_SIG(_effect, int effects, ...)
/* d[sub]image_{rgb16,p8,p4}(..., effects) (no color effect, like dimage()) */
DIMAGE_SIG(, int effects)
/* d[sub]image_{rgb16,p8,p4}_clearbg(..., effects, bg_color_or_index) */
DIMAGE_SIG(_clearbg, int effects, int bg_color_or_index)
/* d[sub]image_{rgb16,p8,p4}_swapcolor(..., effects, source, replacement) */
DIMAGE_SIG(_swapcolor, int effects, int source, int replacement)
/* d[sub]image_{rgb16,p8,p4}_addbg(..., effects, bg_color) */
DIMAGE_SIG(_addbg, int effects, int bg_color)
/* d[sub]image_{rgb16,p8,p4}_dye(..., effects, dye_color) */
DIMAGE_SIG(_dye, int effects, int dye_color)

/* d[sub]image_p4_clearbg_alt(..., effects, bg_index)
   This is functionally identical to CLEARBG, but it uses an alternative
   rendering method that is faster for larger images with wide transparent
   areas. You can swap it with the normal CLEARBG freely. */
DIMAGE_SIG1(p4_clearbg_alt, int effects, int bg_index)

#define dimage_rgb16_effect(x, y, img, eff, ...) \
    dsubimage_rgb16_effect(x, y, img, 0, 0, (img)->width, (img)->height, \
        eff, ##__VA_ARGS__)
#define dimage_p8_effect(x, y, img, eff, ...) \
    dsubimage_p8_effect(x, y, img, 0, 0, (img)->width, (img)->height, \
        eff, ##__VA_ARGS__)
#define dimage_p4_effect(x, y, img, eff, ...) \
    dsubimage_p4_effect(x, y, img, 0, 0, (img)->width, (img)->height, \
        eff, ##__VA_ARGS__)

#undef DIMAGE_SIG
#undef DIMAGE_SIG1

//---
// Clipping utilities
//---

/* Double box specifying both a source and target area */
struct gint_image_box
{
    /* Target location of top-left corner */
    int x, y;
    /* Width and height of rendered sub-image */
    int w, h;
    /* Source bounding box (low included, high excluded) */
    int left, top;
};

/* Clip the provided box against the input. If, after clipping, the box no
   longer intersects the output (whose size is specified as out_w/out_h),
   returns false. Otherwise, returns true. */
bool gint_image_clip_input(image_t const *img, struct gint_image_box *box,
    int out_w, int out_h);

/* Clip the provided box against the output. */
void gint_image_clip_output(struct gint_image_box *b, int out_w, int out_h);

//---
// Internal image rendering routines
//
// The following functions (or non-functions) are implemented in assembler and
// make up the internal interface of the image renderer. If you just want to
// display images, use dimage() and variations; these are only useful if you
// have a different rendering system and wish to use image rendering with
// dynamic effects in it.
//---

/* Renderer command. This structure includes most of the information used by
   the image renderer to perform blits. Some of the information on the target
   is also passed as direct arguments, which is more convenient and slightly
   faster.

   Most of the values here can be set with gint_image_mkcmd(). The last two
   members, along with the return values of the gint_image_FORMAT_loop()
   functions, are used to update the command if one needs to draw *parts* of
   the image and resume the rendering later. This is used in Azur. */
struct gint_image_cmd
{
    /* Shader ID. This is used in Azur, and ignored in gint */
    uint8_t shader_id;
    /* Dynamic effects not already dispatched by renderer
        Bit 0: VFLIP
        Bit 1: HFLIP */
    uint8_t effect;

    /* Number of pixels to render per line. For formats that force either x
       or width alignment (most of them), this is already adjusted to a
       suitable multiple (usually a multiple of 2). */
    int16_t columns;

    /* Stride of the input image (number of pixels between each row), in
       pixels, without subtracting the number of columns */
    int16_t input_stride;

    /* Number of lines in the command. This can be adjusted freely, and is
       particularly useful in Azur for fragmented rendering. */
    uint8_t lines;

    /* [Any effect]: Offset of first edge */
    int8_t edge_1;

    /* Core loop; this is an internal label of the renderer */
    void const *loop;
    /* Output pixel array, offset by target x/y */
    void const *output;
    /* Input pixel array, offset by source x/y. For formats that force x
       alignment, this is already adjusted. */
    void const *input;
    /* Palette, when applicable */
    uint16_t const *palette;

    /* [Any effect]: Offset of right edge */
    int16_t edge_2;
    /* [CLEARBG, SWAPCOLOR]: Source color */
    uint16_t color_1;
    /* [SWAPCOLOR]: Destination color */
    uint16_t color_2;

    /* Remaining height (for updates between fragments) */
    int16_t height;
    /* Local x position (for updates between fragments) */
    int16_t x;
};

/* gint_image_mkcmd(): Prepare a rendering command with dynamic effects

   This function crafts an image renderer command. It loads all the settings
   except for effect-dependent parameters: the [.loop] label, the color section
   of [.effect], and color effect settings. See the effect-specific functions
   to see how they are defined.

   The benefit of this approach is that the rendering code does not need to be
   linked in unless an effect is actually used, which avoids blowing up the
   size of the add-in as the number of support dynamic effects increases.

   @box         Requested on-screen box (will be clipped depending on effects)
   @img         Source image
   @effects     Set of dynamic effects to be applied, as an [IMAGE_*] bitmask
   @left_edge   Whether to force 2-alignment on the input (box->left)
   @right_edge  Whether to force 2-alignment on the width
   @cmd         Command to be filled
   @out_width   Output width (usually DWIDTH)
   @out_height  Output height (usually DHEIGHT)

   Returns false if there is nothing to render because of clipping (in which
   case [cmd] is unchanged), true otherwise. [*box] is also updated to reflect
   the final box after clipping but not accounting for edges.  */
bool gint_image_mkcmd(struct gint_image_box *box, image_t const *img,
    int effects, bool left_edge, bool right_edge,
    struct gint_image_cmd *cmd, int out_width, int out_height);

/* Entry point of the renderers. These functions can be called normally as long
   as you can build the commands (eg. by using gint_image_mkcmd() then filling
   the effect-specific information). */
void *gint_image_rgb16_loop  (int output_width, struct gint_image_cmd *cmd);
void *gint_image_p8_loop     (int output_width, struct gint_image_cmd *cmd);
void *gint_image_p4_loop     (int output_width, struct gint_image_cmd *cmd);

/* Renderer fragments. The following can absolutely not be called from C code
   as they aren't full functions (and this isn't their prototype). These are
   continuations to be specified in the [.loop] field of a command before using
   one of the functions above. */

void gint_image_rgb16_normal(void);
void gint_image_rgb16_clearbg(void);
void gint_image_rgb16_swapcolor(void);
void gint_image_rgb16_dye(void);

void gint_image_p8_normal(void);
void gint_image_p8_clearbg(void);
void gint_image_p8_swapcolor(void);
void gint_image_p8_dye(void);

void gint_image_p4_normal(void);
void gint_image_p4_clearbg(void);
void gint_image_p4_clearbg_alt(void);
void gint_image_p4_swapcolor(void);
void gint_image_p4_dye(void);

//---
// Image library utilities
//
// The following functions and macros are mostly internal utilities; they are
// exposed here in case user applications want to extend the set of image
// transforms with custom additions.
//---

/* image_target(): Check if an image can be used as target for a transform

   This function is used to quickly check whether a transform from [src] to
   [dst] is possible. It requires image_valid(src) and image_valid(dst), plus
   any optional constraints specified as variadic arguments. These constraints
   can be:

   * NOT_P4: fails if [dst] is P4.
   * DATA_RW: fails if [dst] is not data-writable.
   * PALETTE_RW: fails if [dst] is not palette-writable.
   * SAME_SIZE: fails if [dst] is not at least as large as [src].

   For example, in image_hflip(), we write:
     if(!image_target(src, dst, NOT_P4, DATA_RW, SAME_SIZE)) return; */

enum {
    IMAGE_TARGET_NONE,
    IMAGE_TARGET_NOT_P4,
    IMAGE_TARGET_DATA_RW,
    IMAGE_TARGET_PALETTE_RW,
    IMAGE_TARGET_SAME_SIZE,
    IMAGE_TARGET_SAME_FORMAT,
    IMAGE_TARGET_SAME_DEPTH,
};
bool image_target(image_t const *src, image_t *dst, ...);

#define image_target(src, dst, ...) \
    image_target(src, dst, image_target_arg1(__VA_ARGS__ __VA_OPT__(,) NONE))
#define image_target_arg1(c, ...) \
    IMAGE_TARGET_ ## c __VA_OPT__(, image_target_arg2(__VA_ARGS__))
#define image_target_arg2(c, ...) \
    IMAGE_TARGET_ ## c __VA_OPT__(, image_target_arg3(__VA_ARGS__))
#define image_target_arg3(c, ...) \
    IMAGE_TARGET_ ## c __VA_OPT__(, image_target_arg4(__VA_ARGS__))
#define image_target_arg4(c, ...) \
    IMAGE_TARGET_ ## c __VA_OPT__(, image_target_arg5(__VA_ARGS__))
#define image_target_arg5(c, ...) \
    IMAGE_TARGET_ ## c __VA_OPT__(, image_target_arg6(__VA_ARGS__))
#define image_target_arg6(c, ...) \
    IMAGE_TARGET_ ## c __VA_OPT__(, image_target_too_many_args(__VA_ARGS__))

#endif /* FXCG50 */

#ifdef __cplusplus
}
#endif

#endif /* GINT_IMAGE */