Add an `use_hdr` property to GradientTexture to allow storing HDR colors

This is disabled by default to save some memory and preserve the existing
behavior of clamping colors.

doc/classes/GradientTexture.xml

@@ -14,6 +14,9 @@
 		<member name="gradient" type="Gradient" setter="set_gradient" getter="get_gradient">
 			The [Gradient] that will be used to fill the texture.
 		</member>
+		<member name="use_hdr" type="bool" setter="set_use_hdr" getter="is_using_hdr" default="false">
+			If [code]true[/code], the generated texture will support high dynamic range ([constant Image.FORMAT_RGBAF] format). This allows for glow effects to work if [member Environment.glow_enabled] is [code]true[/code]. If [code]false[/code], the generated texture will use low dynamic range; overbright colors will be clamped ([constant Image.FORMAT_RGBA8] format).
+		</member>
 		<member name="width" type="int" setter="set_width" getter="get_width" default="2048">
 			The number of color samples that will be obtained from the [Gradient].
 		</member>

scene/resources/texture.cpp

@@ -1758,11 +1758,16 @@ void GradientTexture::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_gradient"), &GradientTexture::get_gradient);
 
 	ClassDB::bind_method(D_METHOD("set_width", "width"), &GradientTexture::set_width);
+	// The `get_width()` method is already exposed by the parent class Texture2D.
+
+	ClassDB::bind_method(D_METHOD("set_use_hdr", "enabled"), &GradientTexture::set_use_hdr);
+	ClassDB::bind_method(D_METHOD("is_using_hdr"), &GradientTexture::is_using_hdr);
 
 	ClassDB::bind_method(D_METHOD("_update"), &GradientTexture::_update);
 
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "gradient", PROPERTY_HINT_RESOURCE_TYPE, "Gradient"), "set_gradient", "get_gradient");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "width", PROPERTY_HINT_RANGE, "1,4096"), "set_width", "get_width");
+	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "use_hdr"), "set_use_hdr", "is_using_hdr");
 }
 
 void GradientTexture::set_gradient(Ref<Gradient> p_gradient) {
@@ -1800,30 +1805,49 @@ void GradientTexture::_update() {
 		return;
 	}
 
-	Vector<uint8_t> data;
-	data.resize(width * 4);
-	{
-		uint8_t *wd8 = data.ptrw();
+	if (use_hdr) {
+		// High dynamic range.
+		Ref<Image> image = memnew(Image(width, 1, false, Image::FORMAT_RGBAF));
 		Gradient &g = **gradient;
-
+		// `create()` isn't available for non-uint8_t data, so fill in the data manually.
 		for (int i = 0; i < width; i++) {
 			float ofs = float(i) / (width - 1);
-			Color color = g.get_color_at_offset(ofs);
+			image->set_pixel(i, 0, g.get_color_at_offset(ofs));
+		}
 
-			wd8[i * 4 + 0] = uint8_t(CLAMP(color.r * 255.0, 0, 255));
-			wd8[i * 4 + 1] = uint8_t(CLAMP(color.g * 255.0, 0, 255));
-			wd8[i * 4 + 2] = uint8_t(CLAMP(color.b * 255.0, 0, 255));
-			wd8[i * 4 + 3] = uint8_t(CLAMP(color.a * 255.0, 0, 255));
+		if (texture.is_valid()) {
+			RID new_texture = RS::get_singleton()->texture_2d_create(image);
+			RS::get_singleton()->texture_replace(texture, new_texture);
+		} else {
+			texture = RS::get_singleton()->texture_2d_create(image);
+		}
+	} else {
+		// Low dynamic range. "Overbright" colors will be clamped.
+		Vector<uint8_t> data;
+		data.resize(width * 4);
+		{
+			uint8_t *wd8 = data.ptrw();
+			Gradient &g = **gradient;
+
+			for (int i = 0; i < width; i++) {
+				float ofs = float(i) / (width - 1);
+				Color color = g.get_color_at_offset(ofs);
+
+				wd8[i * 4 + 0] = uint8_t(CLAMP(color.r * 255.0, 0, 255));
+				wd8[i * 4 + 1] = uint8_t(CLAMP(color.g * 255.0, 0, 255));
+				wd8[i * 4 + 2] = uint8_t(CLAMP(color.b * 255.0, 0, 255));
+				wd8[i * 4 + 3] = uint8_t(CLAMP(color.a * 255.0, 0, 255));
+			}
 		}
-	}
 
-	Ref<Image> image = memnew(Image(width, 1, false, Image::FORMAT_RGBA8, data));
+		Ref<Image> image = memnew(Image(width, 1, false, Image::FORMAT_RGBA8, data));
 
-	if (texture.is_valid()) {
-		RID new_texture = RS::get_singleton()->texture_2d_create(image);
-		RS::get_singleton()->texture_replace(texture, new_texture);
-	} else {
-		texture = RS::get_singleton()->texture_2d_create(image);
+		if (texture.is_valid()) {
+			RID new_texture = RS::get_singleton()->texture_2d_create(image);
+			RS::get_singleton()->texture_replace(texture, new_texture);
+		} else {
+			texture = RS::get_singleton()->texture_2d_create(image);
+		}
 	}
 
 	emit_changed();
@@ -1839,6 +1863,19 @@ int GradientTexture::get_width() const {
 	return width;
 }
 
+void GradientTexture::set_use_hdr(bool p_enabled) {
+	if (p_enabled == use_hdr) {
+		return;
+	}
+
+	use_hdr = p_enabled;
+	_queue_update();
+}
+
+bool GradientTexture::is_using_hdr() const {
+	return use_hdr;
+}
+
 Ref<Image> GradientTexture::get_image() const {
 	if (!texture.is_valid()) {
 		return Ref<Image>();

scene/resources/texture.h

@@ -686,6 +686,7 @@ private:
 	bool update_pending = false;
 	RID texture;
 	int width = 2048;
+	bool use_hdr = false;
 
 	void _queue_update();
 	void _update();
@@ -700,6 +701,9 @@ public:
 	void set_width(int p_width);
 	int get_width() const override;
 
+	void set_use_hdr(bool p_enabled);
+	bool is_using_hdr() const;
+
 	virtual RID get_rid() const override { return texture; }
 	virtual int get_height() const override { return 1; }
 	virtual bool has_alpha() const override { return true; }