Function DrawSliderWidget

src/slider.cpp:34–82

* Draw a slider widget with knob at given value * @param r Rectangle to draw the widget in * @param wedge_colour Colour to draw wedge. * @param handle_colour Colour to draw handle. * @param text_colour Colour of text. * @param min_value Minimum value of slider * @param max_value Maximum value of slider * @param nmarks Number of marks to display (when mark_func is provided.) * @param value

 * @param mark_func Callback function to get the StringID to draw on a mark.
 */
void DrawSliderWidget(Rect r, Colours wedge_colour, Colours handle_colour, TextColour text_colour, int min_value, int max_value, int nmarks, int value, SliderMarkFunc *mark_func)
{
	/* Allow space for labels. We assume they are in the small font. */
	if (mark_func != nullptr) r.bottom -= GetCharacterHeight(FS_SMALL) + WidgetDimensions::scaled.hsep_normal;

	max_value -= min_value;

	/* Draw a wedge indicating low to high value. */
	const int ha = (r.bottom - r.top) / 5;
	const int sw = ScaleGUITrad(SLIDER_WIDTH);
	const int t = WidgetDimensions::scaled.bevel.top; /* Thickness of lines */
	int wx1 = r.left  + sw / 2;
	int wx2 = r.right - sw / 2;
	if (_current_text_dir == TD_RTL) std::swap(wx1, wx2);
	const PixelColour shadow = GetColourGradient(wedge_colour, SHADE_DARK);
	const PixelColour fill = GetColourGradient(wedge_colour, SHADE_LIGHTER);
	const PixelColour light = GetColourGradient(wedge_colour, SHADE_LIGHTEST);
	const std::array<Point, 3> wedge{ Point{wx1, r.bottom - ha}, Point{wx2, r.top + ha}, Point{wx2, r.bottom - ha} };
	GfxFillPolygon(wedge, fill);
	GfxDrawLine(wedge[0].x, wedge[0].y, wedge[2].x, wedge[2].y, light, t);
	GfxDrawLine(wedge[1].x, wedge[1].y, wedge[2].x, wedge[2].y, _current_text_dir == TD_RTL ? shadow : light, t);
	GfxDrawLine(wedge[0].x, wedge[0].y, wedge[1].x, wedge[1].y, shadow, t);

	int x;
	if (mark_func != nullptr) {
		for (int mark = 0; mark < nmarks; ++mark) {
			const int mark_value = (max_value * mark) / (nmarks - 1);

			auto str = mark_func(nmarks, mark, mark_value + min_value);
			if (!str.has_value()) continue;

			x = mark_value;
			if (_current_text_dir == TD_RTL) x = max_value - mark_value;
			x = r.left + (x * (r.right - r.left - sw) / max_value) + sw / 2;
			GfxDrawLine(x, r.bottom - ha + 1, x, r.bottom + (str->empty() ? 0 : WidgetDimensions::scaled.hsep_normal), shadow, t);
			if (str->empty()) continue;

			Dimension d = GetStringBoundingBox(*str, FS_SMALL);
			x = Clamp(x - d.width / 2, r.left, r.right - d.width);
			DrawString(x, x + d.width, r.bottom + 1 + WidgetDimensions::scaled.hsep_normal, *str, text_colour, SA_CENTER, false, FS_SMALL);
		}
	}

	/* Draw a slider handle indicating current value. */
	value -= min_value;
	if (_current_text_dir == TD_RTL) value = max_value - value;
	x = r.left + (value * (r.right - r.left - sw) / max_value);
	DrawFrameRect(x, r.top, x + sw, r.bottom, handle_colour, {});
}

/**
 * Handle click on a slider widget to change the value