Tk_AllocColorFromObj(3tk)

💖 Tk_AllocColorFromObj — the Tk Library Procedures glow-up 💖

okay bestie, so this is the manual page for a whole little squad of Tk color functions — Tk_AllocColorFromObj(3tk) and its friends — and yes it's from the Tk Library Procedures collection. We're gonna go through every single one of them, no skips, no skimming, because color management is genuinely iconic when you get it. 🎨✨

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✨ NAME ✨

Tk_AllocColorFromObj, Tk_GetColor, Tk_GetColorFromObj, Tk_GetColorByValue, Tk_NameOfColor, Tk_FreeColorFromObj, Tk_FreeColor — maintaining the database of colors. it's giving color bureaucracy but make it cute 💅

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🌸 SYNOPSIS 🌸

#include <tk.h>

XColor *
Tk_AllocColorFromObj(interp, tkwin, objPtr)

XColor *
Tk_GetColor(interp, tkwin, name)

XColor *
Tk_GetColorFromObj(tkwin, objPtr)

XColor *
Tk_GetColorByValue(tkwin, prefPtr)

const char *
Tk_NameOfColor(colorPtr)

GC
Tk_GCForColor(colorPtr, drawable)

Tk_FreeColorFromObj(tkwin, objPtr)

Tk_FreeColor(colorPtr)

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🎀 ARGUMENTS 🎀

• Tcl_Interp *interp (in) — the interpreter we use for error reporting, so if something goes wrong she's the one who tells you about it 🗣️
• Tk_Window tkwin (in) — the token for the window where this color is gonna be used.
• Tcl_Obj *objPtr (in/out) — a string value that describes the color you want. Lowkey important: her internal rep gets modified to cache a pointer to the corresponding (XColor *). she remembers things 💅
• const char *name (in) — same as objPtr, except the color description comes in as a plain string and the resulting (XColor *) does not get cached. no memory, just vibes.
• XColor *prefPtr (in) — tells you the red, green, and blue intensities of the color you're asking for.
• XColor *colorPtr (in) — pointer to X color info. It must have been allocated by a previous call to Tk_AllocColorFromObj, Tk_GetColor or Tk_GetColorByValue — except when you're passing it to Tk_NameOfColor, where the rules are looser 🫶
• Drawable drawable (in) — the drawable where the resulting graphics context is gonna be used. It must have the same screen and depth as the window the color was allocated for, no exceptions bestie.

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🦋 DESCRIPTION 🦋

These procedures manage the colors your Tk application is using. They let colors be shared whenever possible, so colormap space gets preserved, and when colormap space is all used up they pick the closest available colors. resourceful queens 👑

Given a textual description of a color, Tk_AllocColorFromObj locates a pixel value you can use to render that color in a particular window. The desired color is specified with a value whose string value has to be one of these forms:

• colorname — any of the valid textual names for a color defined in the server's color database file, like red or PeachPuff. (yes, PeachPuff is real and she's gorgeous 🍑)
• #RGB
• #RRGGBB
• #RRRGGGBBB
• #RRRRGGGGBBBB — a numeric spec of the red, green, and blue intensities used to display the color. Each R, G, or B is a single hexadecimal digit. These four forms let you specify colors with 4-bit, 8-bit, 12-bit or 16-bit values. When you provide fewer than 16 bits for each color, they represent the most significant bits of the color, and the lower unfilled bits get repeatedly replicated from the available higher bits. Example bestie: #3a7 is the same as #3333aaaa7777. the way that math just works?? 🔥

Tk_AllocColorFromObj returns a pointer to an XColor structure. That structure tells you the exact intensities of the allocated color (which might differ slightly from what you asked for, depending on the screen's limitations — she does her best) and a pixel value you can draw with in tkwin. If an error happens in Tk_AllocColorFromObj (like an unknown color name, embarrassing), then NULL is returned and an error message gets stored in interp's result if interp is not NULL. If the colormap for tkwin is full, Tk_AllocColorFromObj will just use the closest existing color in the colormap. improvise, adapt, slay. And Tk_AllocColorFromObj caches info about the return value in objPtr, which speeds up future calls to procedures like Tk_AllocColorFromObj and Tk_GetColorFromObj. ⚡

Tk_GetColor is identical to Tk_AllocColorFromObj except the description of the color is specified with a string instead of a value. That means Tk_GetColor can't cache the return value, so Tk_GetColor is less efficient than Tk_AllocColorFromObj. no cache, no speed, still valid tho 🙈

Tk_GetColorFromObj returns the token for an existing color, given the window and description used to create that color. Important: Tk_GetColorFromObj does not actually create the color. It must already have been created with a previous call to Tk_AllocColorFromObj or Tk_GetColor. The return value is cached in objPtr, which speeds up future calls to Tk_GetColorFromObj with the same objPtr and tkwin. she's a lookup girlie, not a maker girlie 💅

Tk_GetColorByValue is similar to Tk_GetColor except the desired color is indicated with the red, green, and blue fields of the structure pointed to by colorPtr.

This package maintains a database of all the colors currently in use. If the same color is requested multiple times from Tk_GetColor or Tk_AllocColorFromObj (say, by different windows), or if the same intensities are requested multiple times from Tk_GetColorByValue, then existing pixel values get re-used. Re-using an existing pixel avoids any interaction with the window server, which makes the allocation much more efficient. These procedures also give you a portable interface that works across all platforms. That's why you should generally use Tk_AllocColorFromObj, Tk_GetColor, or Tk_GetColorByValue instead of lower level procedures like XAllocColor. she's the main character, XAllocColor is the group chat lurker ✨

⚠️ Since different calls to this package may return the same shared pixel value, callers should never change the color of a pixel returned by these procedures. If you need to change a color value dynamically, you should use XAllocColorCells to allocate the pixel value for the color. do not touch, bestie, i'm so serious 😭

The procedure Tk_NameOfColor is roughly the inverse of Tk_GetColor. If its colorPtr argument was created by Tk_AllocColorFromObj or Tk_GetColor, then the return value is the string that was used to create the color. If colorPtr was created by a call to Tk_GetColorByValue, or by any other mechanism, then the return value is a string that could be passed to Tk_GetColor to return the same color. Note: the string returned by Tk_NameOfColor is only guaranteed to persist until the next call to Tk_NameOfColor. so like, screenshot it while you can 📸

Tk_GCForColor returns a graphics context whose foreground field is the pixel allocated for colorPtr and whose other fields all have default values. This is an easy way to do basic drawing with a color. The graphics context is cached with the color and will exist only as long as colorPtr exists; it gets freed when the last reference to colorPtr is freed by calling Tk_FreeColor. ride or die, literally 🫶

When a color is no longer needed, Tk_FreeColorFromObj or Tk_FreeColor should be called to release it. For Tk_FreeColorFromObj the color to release is specified with the same information used to create it; for Tk_FreeColor the color to release is specified with a pointer to its XColor structure. There should be exactly one call to Tk_FreeColorFromObj or Tk_FreeColor for each call to Tk_AllocColorFromObj, Tk_GetColor, or Tk_GetColorByValue. one in, one out, balanced queen ⚖️

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👑 KEYWORDS 👑

color, intensity, value, pixel value

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okay that's the whole page, you ate that 💖 this was Tk 8.1, and the page itself is Tk_AllocColorFromObj(3tk). go forth and allocate responsibly, bestie 🌈🦋✨