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Documentation Index

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LWXGL provides two foundational element types for rendering static visual content: text labels drawn with the 9x15 bitmap font, and filled rectangles used for panels, dividers, or decorative backgrounds. Both elements are identified by an integer ID and rendered on every call to GRenderWindow. This page also covers the shared management functions GDeleteElement and GElemModifyBounds, which apply to every element type in the library.

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GCreateText

void GCreateText(int id, int x, int y, int color, const char* text);
Creates a text label element, or replaces any existing element at the given id. The text is rendered using the 9x15 bitmap font built into the X11 server. Multi-line strings are supported — each \n character advances rendering to the next line, 16 pixels lower. Only a single foreground palette color is applied; there is no background fill for text elements (the window background or a GCreateRect element beneath it provides the background).
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id
int
required
Element slot index. If an element already exists at this ID it is freed and replaced.
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x
int
required
X coordinate of the left edge of the text, in pixels from the window’s top-left corner.
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y
int
required
Y coordinate of the text’s first line. The renderer adds 11 pixels internally before drawing the first line, so y=0 places the top of the first glyph near the top of the window.
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color
int
required
Palette index (0–15) for the text foreground color.
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text
const char*
required
Null-terminated string to display. Embed \n characters for multi-line output. The pointer is stored directly — do not free or mutate the string after passing it.
Each line of a multi-line string is rendered 16 pixels below the previous one. Line spacing is fixed at 16 pixels regardless of font size.

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GCreateRect

void GCreateRect(int id, int x, int y, int w, int h, int fg, int bg);
Creates a filled rectangle element, or replaces any existing element at the given id. The rectangle is drawn in two passes: first the interior fill using bg, then a one-pixel border outline using fg. Either pass can be suppressed by passing -1 for the corresponding color parameter.
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id
int
required
Element slot index. If an element already exists at this ID it is freed and replaced.
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x
int
required
X coordinate of the rectangle’s top-left corner.
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y
int
required
Y coordinate of the rectangle’s top-left corner.
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w
int
required
Width of the rectangle in pixels.
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h
int
required
Height of the rectangle in pixels.
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fg
int
required
Palette index (0–15) for the border outline. Pass -1 to skip drawing the border entirely.
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bg
int
required
Palette index (0–15) for the interior fill. Pass -1 to skip the fill (transparent interior).
Use fg=-1 with a solid bg for a plain filled panel with no border. Use bg=-1 with a solid fg for a hollow rectangle outline over whatever is rendered beneath it.

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Shared Element Management

These functions work on any element type created through LWXGL, not just text and rectangles.

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GDeleteElement

void GDeleteElement(int index);
Frees the element at the given index and sets its slot to NULL. For image elements, the backing XImage and pixel buffers (data and prev) are also released before freeing the element. Calling this on an already-null or out-of-range slot is a no-op.
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index
int
required
Element slot index to free.
After calling GDeleteElement, any pointer previously returned by GGetImageData or GGetInput for that ID becomes invalid. Do not dereference such pointers after deletion.

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GElemModifyBounds

void GElemModifyBounds(int id, int x, int y, int w, int h);
Updates the position and dimensions of an existing element without recreating it. The change takes effect on the next call to GRenderWindow. This is more efficient than destroying and recreating an element just to reposition it.
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id
int
required
Element slot index to update.
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x
int
required
New X coordinate.
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y
int
required
New Y coordinate.
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w
int
required
New width in pixels. For text elements, w and h are unused by the renderer, but the values are still stored.
​
h
int
required
New height in pixels.

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Example

The following example creates a gray panel rectangle and overlays a white title label onto it. Element IDs 0 and 1 are used — IDs are arbitrary non-negative integers you manage yourself. 
#include "libLWXGL.h"

void setup(void) {
    /* Draw a dark gray filled panel at (20, 20), 300x40 pixels.
       fg=7 (light gray border), bg=8 (dark gray fill) */
    GCreateRect(0, 20, 20, 300, 40, 7, 8);

    /* Place a white text label inside the panel.
       color=15 (white) */
    GCreateText(1, 30, 28, 15, "LWXGL Demo Panel");
}

void on_frame(int frame) {
    /* Slide the panel 1 pixel to the right every other frame */
    if (frame % 2 == 0) {
        GElemModifyBounds(0, 20 + frame / 2, 20, 300, 40);
        GElemModifyBounds(1, 30 + frame / 2, 28, 0, 0);
    }
}

int main(void) {
    GCreateWindow(640, 480, "Text & Rect Demo", 0);
    setup();
    GSimpleWindowLoop(60, on_frame);
    GDeleteWindow();
    return 0;
}

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