Various fixes and documentation for CanvasGroup

Properly apply custom materials with CanvasGroups in the GLES3 backend

Properly blur backbuffer when using a partial rect in forward_plus and
gl_compatibility renderers

Properly set fit_margin when clear_margin is set

Fix shader error during backbuffer clear in mobile renderer

1 files changed, 17 insertions, 0 deletions

diff --git a/doc/classes/CanvasGroup.xml b/doc/classes/CanvasGroup.xml
index d2bcf3c7ac..37827defec 100644
--- a/doc/classes/CanvasGroup.xml
+++ b/doc/classes/CanvasGroup.xml
@@ -5,16 +5,33 @@
 	</brief_description>
 	<description>
 		Child [CanvasItem] nodes of a [CanvasGroup] are drawn as a single object. It allows to e.g. draw overlapping translucent 2D nodes without blending (set [member CanvasItem.self_modulate] property of [CanvasGroup] to achieve this effect).
+		[b]Note:[/b] The [CanvasGroup] uses a custom shader to read from the backbuffer to draw its children. Assigning a [Material] to the [CanvasGroup] overrides the builtin shader. To duplicate the behavior of the builtin shader in a custom [Shader] use the following:
+		[codeblock]
+		shader_type canvas_item;
+
+		void fragment() {
+		    vec4 c = textureLod(SCREEN_TEXTURE, SCREEN_UV, 0.0);
+
+		    if (c.a &gt; 0.0001) {
+		        c.rgb /= c.a;
+		    }
+
+		    COLOR *= c;
+		}
+		[/codeblock]
 		[b]Note:[/b] Since [CanvasGroup] and [member CanvasItem.clip_children] both utilize the backbuffer, children of a [CanvasGroup] who have their [member CanvasItem.clip_children] set to anything other than [constant CanvasItem.CLIP_CHILDREN_DISABLED] will not function correctly.
 	</description>
 	<tutorials>
 	</tutorials>
 	<members>
 		<member name="clear_margin" type="float" setter="set_clear_margin" getter="get_clear_margin" default="10.0">
+			Sets the size of the margin used to expand the clearing rect of this [CanvasGroup]. This expands the area of the backbuffer that will be used by the [CanvasGroup]. A smaller margin will reduce the area of the backbuffer used which can increase performance, however if [member use_mipmaps] is enabled, a small margin may result in mipmap errors at the edge of the [CanvasGroup]. Accordingly, this should be left as small as possible, but should be increased if artifacts appear along the edges of the canvas group.
 		</member>
 		<member name="fit_margin" type="float" setter="set_fit_margin" getter="get_fit_margin" default="10.0">
+			Sets the size of a margin used to expand the drawable rect of this [CanvasGroup]. The size of the [CanvasGroup] is determined by fitting a rect around its children then expanding that rect by [member fit_margin]. This increases both the backbuffer area used and the area covered by the [CanvasGroup] both of which can reduce performance. This should be kept as small as possible and should only be expanded when an increased size is needed (e.g. for custom shader effects).
 		</member>
 		<member name="use_mipmaps" type="bool" setter="set_use_mipmaps" getter="is_using_mipmaps" default="false">
+			If [code]true[/code], calculates mipmaps for the backbuffer before drawing the [CanvasGroup] so that mipmaps can be used in a custom [ShaderMaterial] attached to the [CanvasGroup]. Generating mipmaps has a performance cost so this should not be enabled unless required.
 		</member>
 	</members>
 </class>