Add support for setting corner radius per corner

[Feodor0090]

... i.e. now you can have 3 corners with radius 100 and the 4th with 10, for example.

Half-broken and non-mergeable at this state. Game probably won't run due to transforms.

If the direction is ok, i need help with bounding box calculation (now it calculates using the biggest radius) and uniforms buffer - there are too many paddings and idk how to rearrange the fields so nothing breaks.
Also, non-rounded borders and rounded renders in different manner so their combination looks weird. Didn't understand what to do with this too.

(bottom one is 0/50, top one is 5/50, notice the step where rounding begins)

xmldocs and interpolations will be done later. done

[bdach]

Previously: #3652 (comment)

[Feodor0090]

While messing with edge effect rendering code, all that i managed to learn is that bottom-right quarter size is left unchanged from actual container size, and top-left quarters are growing in size so that glow "overrun" is equal to effect radius. Removing inflation in RectangleF effectRect = maskingInfo.Value.MaskingRect.Inflate(edgeEffect.Radius).Offset(edgeEffect.Offset); makes this work as expected, adding -Radius (shrinking) makes edge overruns to top-left quarter.

There is obviously something with either UV or g_MaskingRect, so i randomly did

diff --git a/osu.Framework/Resources/Shaders/sh_Masking.h b/osu.Framework/Resources/Shaders/sh_Masking.h
index e9190362a..68fd25ce1 100644
--- a/osu.Framework/Resources/Shaders/sh_Masking.h
+++ b/osu.Framework/Resources/Shaders/sh_Masking.h
@@ -63,7 +63,7 @@ lowp vec4 getBorderColour()
 
 highp float getCornerRadius()
 {
-       highp vec2 relativeTexCoord = v_MaskingPosition / (g_MaskingRect.zw - g_MaskingRect.xy);
+       highp vec2 relativeTexCoord = v_MaskingPosition / ((g_MaskingRect.zw - g_MaskingRect.xy)-vec2(g_MaskingBlendRange*2, g_MaskingBlendRange*2));
        highp float top = mix(g_CornerRadius.x, g_CornerRadius.z, step(0.5, relativeTexCoord.x));
        highp float bottom = mix(g_CornerRadius.y, g_CornerRadius.w, step(0.5, relativeTexCoord.x));
        return mix(top, bottom, step(0.5, relativeTexCoord.y));
@@ -71,7 +71,7 @@ highp float getCornerRadius()
 
 highp float getInnerCornerRadius()
 {
-       highp vec2 relativeTexCoord = v_MaskingPosition / (g_MaskingRect.zw - g_MaskingRect.xy);
+       highp vec2 relativeTexCoord = v_MaskingPosition / ((g_MaskingRect.zw - g_MaskingRect.xy)-vec2(g_MaskingBlendRange*2, g_MaskingBlendRange*2));
        highp float top = mix(g_InnerCornerRadius.x, g_InnerCornerRadius.z, step(0.5, relativeTexCoord.x));
        highp float bottom = mix(g_InnerCornerRadius.y, g_InnerCornerRadius.w, step(0.5, relativeTexCoord.x));
        return mix(top, bottom, step(0.5, relativeTexCoord.y));

and...

... it works?

Is this even a valid fix?