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Documentation Index

Fetch the complete documentation index at: https://mintlify.com/DRESsedAlarm184/LWXGL/llms.txt

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Rectangle and ellipse elements are the simplest persistent drawing primitives in LWXGL. Each is defined by a bounding box and a pair of colors: fg controls the border (outline) and bg controls the fill. Setting either to CLR_NONE (-1) skips that draw operation entirely, allowing filled shapes without borders, outlined shapes without fills, or both. Both types can be repositioned and resized at any time using ElemModifyBounds.

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Color Semantics

ParameterRoleRenders via
fgBorder / outlineXDrawRectangle / XDrawArc
bgFillXFillRectangle / XFillArc
Pass CLR_NONE (-1) for either parameter to suppress that draw call. Both CLR_NONE is legal but produces an invisible element.

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Functions

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CreateRect

Creates a persistent rectangle element. On each frame, LWXGL first fills the interior (if bg is not CLR_NONE) and then draws the one-pixel border (if fg is not CLR_NONE). 
void CreateRect(int id, int x, int y, int w, int h, int fg, int bg);
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id
int
required
Unique integer identifier for this element.
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x
int
required
Left edge of the rectangle in pixels.
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y
int
required
Top edge of the rectangle in pixels.
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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
Border color, one of the CLR_* constants. Pass CLR_NONE for no border.
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bg
int
required
Fill color, one of the CLR_* constants. Pass CLR_NONE for no fill (transparent).
Known rendering bug in CreateRect: The internal renderer passes e->y (the element’s top-edge position) as the height argument to ImmediateRect instead of e->h. The call in renderer.cc is:
ImmediateRect(e->x, e->y, e->w, e->y, rect->fg, rect->bg);
//                                ^^^^ bug: should be e->h
This means the rendered rectangle’s height equals its Y position, not the height you passed to CreateRect. The h parameter you provide has no effect on the rendered output.As a workaround, draw rectangles directly from your on_every callback using ImmediateRect, which does not have this bug:
// Instead of CreateRect, call this from on_every:
ImmediateRect(x, y, w, h, fg, bg);
CreateEllipse is not affected by this bug — its renderer correctly forwards all four bounding-box values.

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CreateEllipse

Creates a persistent ellipse (or circle) element inscribed within the given bounding box. The full 360° arc is drawn using XFillArc and XDrawArc. 
void CreateEllipse(int id, int x, int y, int w, int h, int fg, int bg);
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id
int
required
Unique integer identifier for this element.
​
x
int
required
Left edge of the bounding box in pixels.
​
y
int
required
Top edge of the bounding box in pixels.
​
w
int
required
Width of the bounding box in pixels. Set equal to h for a perfect circle.
​
h
int
required
Height of the bounding box in pixels.
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fg
int
required
Outline color, one of the CLR_* constants. Pass CLR_NONE for no outline.
​
bg
int
required
Fill color, one of the CLR_* constants. Pass CLR_NONE for no fill.

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ElemModifyBounds

Repositions or resizes any element, including rectangles and ellipses. Pass -1 for w or h to leave the corresponding dimension unchanged. 
void ElemModifyBounds(int id, int x, int y, int w, int h);
​
id
int
required
The identifier of the element to modify.
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x
int
required
New x position (left edge).
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y
int
required
New y position (top edge).
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w
int
required
New width, or -1 to keep the current width.
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h
int
required
New height, or -1 to keep the current height.

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Code Examples

#include "libLWXGL.h"

static void on_frame(int tick, float dt) { (void)tick; (void)dt; }

int main(void) {
    CreateWindow(500, 300, "Shapes Demo", CLR_BLACK, FLAG_NONE);

    /*
     * NOTE: CreateRect has a known height-rendering bug (see Warning above).
     * The 'h' parameter has no effect; rendered height equals the y position.
     * Use ImmediateRect in on_every for correct rectangle rendering.
     */

    /* 1. Bordered rectangle: white fill, gray border */
    CreateRect(1, 20, 20, 160, 80, CLR_GRAY, CLR_WHITE);

    /* 2. Filled rectangle with no border (solid panel) */
    CreateRect(2, 200, 20, 160, 80, CLR_NONE, CLR_BLUE);

    /* 3. Outline-only rectangle (transparent interior) */
    CreateRect(3, 380, 20, 100, 80, CLR_YELLOW, CLR_NONE);

    /* 4. Ellipse (wide oval): cyan fill, white outline */
    CreateEllipse(4, 20, 130, 200, 80, CLR_WHITE, CLR_CYAN);

    /* 5. Perfect circle (w == h): magenta fill, no outline */
    CreateEllipse(5, 240, 130, 80, 80, CLR_NONE, CLR_MAGENTA);

    /* 6. Outline-only circle */
    CreateEllipse(6, 340, 130, 80, 80, CLR_LGREEN, CLR_NONE);

    /* Move element 1 to a new position after creation */
    ElemModifyBounds(1, 20, 220, -1, -1);

    MainWindowLoop(60, on_frame);
    TerminateWindow();
    return 0;
}
To animate a shape, call ElemModifyBounds from inside your on_every callback each frame, updating x or y based on GetElapsedTime() or delta_time.

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