How to hide/show the underline of link text on mouse hover

I want my link text to show their underline only when the mouse is hovering over them. Based on the code I found in another thread, and the example code for reacting to mouse hover (TMP_TextSelector_B.cs) I have made my own code.

My problem is that the underline doesn't match the look of the text. If the text has outline and "drop shadow" effects, those do not automatically apply on the underline I make since I'm only making them with simple mesh generation code.

I notice that in TextMeshPro's TMP_Text.cs it has a DrawUnderlineMesh method. Is there somehow a way to get the vertex indices of those underline meshes? Hiding and showing would (hopefully) be a simple matter of setting their vertex color alpha to 0.

So instead of making my own underline meshes I could just use the existing underline mesh generated by TMP. The only thing I like about the custom generated underline mesh that I have right now is that it will be easy to make underlines that have a dotted line pattern.

I am on Unity 2018.4 and using TextMesh Pro 1.4.1 if that matters.

 

Could you clarify what "segment" means? I tried getting the last character index of a link's text, multiply that by 4 since they're quads, then setting the alpha value of the next 12 colors from that, but I end up changing the wrong thing.

I am also wondering about the output of my debug log. characterInfo Length is 128, but the colors Length when divided by 4 (because they're quads I assume) is only 121 (value changes depending on how much word-wrapped the text is).

Code (CSharp):

1.  
2. void ShowUnderline(bool show, int linkIndex)
3. {
4.   var textInfo = m_TextComponent.textInfo;
5.   var linkInfo = textInfo.linkInfo[linkIndex];
6.   var lastCharIndex = linkInfo.linkTextfirstCharacterIndex + linkInfo.linkTextLength - 1;
7.  
8.   int materialIndex = textInfo.characterInfo[lastCharIndex].materialReferenceIndex;
9.   var colors = textInfo.meshInfo[materialIndex].colors32;
10.  
11.   Debug.Log($"link text: \"{linkInfo.GetLinkText()}\" last char: {textInfo.characterInfo[lastCharIndex].character} (index: {lastCharIndex} of {textInfo.characterInfo.Length}) colors length: {colors.Length} per 4: {colors.Length/4}");
12.  
13.   // each underline is 12 vertices, and starts after the last character
14.   int indexX4 = (lastCharIndex+1) * 4;
15.   var alphaValue = show ? byte.MaxValue : byte.MinValue;
16.   colors[indexX4 + 0].a = alphaValue;
17.   colors[indexX4 + 1].a = alphaValue;
18.   colors[indexX4 + 2].a = alphaValue;
19.   colors[indexX4 + 3].a = alphaValue;
20.  
21.   colors[indexX4 + 4].a = alphaValue;
22.   colors[indexX4 + 5].a = alphaValue;
23.   colors[indexX4 + 6].a = alphaValue;
24.   colors[indexX4 + 7].a = alphaValue;
25.  
26.   colors[indexX4 + 8].a = alphaValue;
27.   colors[indexX4 + 9].a = alphaValue;
28.   colors[indexX4 + 10].a = alphaValue;
29.   colors[indexX4 + 11].a = alphaValue;
30.  
31.   m_TextComponent.UpdateVertexData(TMP_VertexDataUpdateFlags.Colors32);
32. }
33.  

 

I kind of understand the theory behind what you said, but I know so little about TMP_TextInfo, and TMP_CharacterInfo and the other Info structs, I have no idea where to begin. I've only been looking through the TMP source code and guessing which field I need to use. I'm gonna have to put this on hold and return to it when I have time.