Text Contrast on Calender Entry

[FloBab73]

Checklist

• I can reproduce the bug with the latest version given here.
• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
• This issue contains only one bug.
• I have read and understood the contribution guidelines.

Affected app version

1.9.0

Affected Android/Custom ROM version

Android 16

Affected device model

Pixel 10

How did you install the app?

F-Droid / IzzyOnDroid

Which calendar service or provider do you use, if any?

No response

Which sync adapter app do you use for calendar synchronization, if any?

No response

Steps to reproduce the bug

Create a new Event and set the color to #9AD8B5 (left)
Create a new Event and set the color to #66C791 (right)

Expected behavior

The text on the right is black

Actual behavior

The text on the right is white

Screenshots/Screen recordings

link

Additional information

I understand that the text color changes depending on the color (left event), but it seems that the decision is not correct, as seen from the pictures above.
The behaviour is independent of whether the rest of the app is in light or dark mode

[rros]

I looked at this issue and currently the way the color is determined is based on a luminance threshold.

fun Int.getContrastColor(): Int {
    val luminance = ColorUtils.calculateLuminance(this)
    return if (luminance > 0.5) DARK_GREY else Color.WHITE
}

This method does not work for every color combination as you have found.

Also the app uses either dark grey (#333333) or white (#FFFFFF). I think black (#000000) has always a better contrast on light backgrounds compared to dark grey. I.e. in your example this is the contrast for dark grey:

Android has actually a method to calculate the contrast ratio ColorUtils#calculateContrast(int,int). My suggestion would be to change the implementation of getContrastColor() to calculate the contrast ratios for white and black against the background color and return the one that has the highest contrast ratio.

[rros]

I did a quick test and this method calculate exactly the same values as in the pictures above. With the following code:

val contrastWhite = ColorUtils.calculateContrast(Color.WHITE, event.color)
val contrastBlack = ColorUtils.calculateContrast(Color.BLACK, event.color)
var paintColor = if (contrastBlack > contrastWhite) Color.BLACK else Color.WHITE

I get the following result:

To implement this properly, I think this must be changed in the getContrastColor in commons extensions. I can make a PR for this in the commons project if you like @naveensingh

[rros]

I just created a PR in the commons project to change the implementation of getContrastColor(). I also added an overload so we can actually use different colors like Black and White.

Also it is better to first determine if the alpha-channel must be adjusted before choosing the better contrasting color. So when this PR is merged, the implementation for getEventTitlePaint() should be changed to something like this:

    private fun getEventTitlePaint(event: MonthViewEvent): Paint {
        val adjustAlpha = when {
            event.isTask -> dimCompletedTasks && event.isTaskCompleted
            else -> dimPastEvents && event.isPastEvent && !isPrintVersion
        }

        var alpha = if (adjustAlpha) HIGHER_ALPHA else 1f
        var white = Color.WHITE.adjustAlpha(alpha)
        var black = Color.BLACK.adjustAlpha(alpha)

        var paintColor = event.color.getContrastColor(black, white)

        val curPaint = Paint(eventTitlePaint)
        curPaint.color = paintColor
        curPaint.isStrikeThruText = event.shouldStrikeThrough()
        return curPaint
    }

[naveensingh]

Closing as per #1065 (comment)