Feature Request: Add retro Apple II cursor style about terminal HOT 2 CLOSED

Our most commonly used cursor "color" is one that inverses the underlying color to always keep it visible:

However, there's a problem: If the underlying color is very close to gray (or some equivalent) then the inverse will also be gray which causes the cursor to be invisible. To solve that issue, we compute color distances when drawing the cursor and nudge the cursor and inverted text colors to be further apart. Finally, we also need to stretch the cursor when hovering over a wide glyph and it's unclear how that would look like with this grid shape.

While the 5x5 grid glyph can technically be implemented just like the empty box cursor as a set of rectangles, this one would result in not just 4 but 25 rectangles. Every single one of those would consist of 2 individual triangles during rendering. That's certainly anything but optimal.

The proper solution here would be to draw the glyph into our glyph cache and use it as a pixel-by-pixel lookup texture to invert every underlying pixel where the lookup texture is lit/white. This would need to be implemented in the pixel shader. But there's multiple problems with that:

• Requires us to port the color distance algorithm to HLSL.
• Requires us to invert the text at the time it is being blended into the swap chain. This is because text rendering is gamma corrected based on the text color and this information is lost once the blending finished. Inverting the color retroactively leads to either too thin or too fat looking stems in the glyphs.
• Right now, we upload the pixel shader constant buffer as an immutable buffer, which is quite efficient. This change would require us to turn that into a dynamic buffer because the constant buffer would need to store the changing location of the cursor in the viewport. Graphics drivers may handle dynamic constant buffers by allocating large ring buffers so that they can be efficiently pipelined. We'll have to test all of our relevant hardware on how they react to such a change. After all, we're trying to optimize the renderer for power draw and memory usage, while graphics drivers are always trying to optimize us as if we were a video game. This conflict of interests continues to be an issue for us.

I think rendering cursor in the pixel shader is the right way to do it, no matter what. The importance of this feature VS the time required for testing it is the real issue unfortunately. 😟

from terminal.

@lhecker
Hey, I know that segmented 0! 😉

Thanks for all the details. And yeah, I was hoping it could just be an extra label and character in a list of cursors.
I didn't think about the way you invert the character under the cursor.
On the Apple II, the cursor is not xor-blitted with the character at that position, it simply toggles between the character and the cursor. So I was thinking about that behavior which is basically just changing the character at the cursor position on the blink interval.
The work involved isn't worth it for the nostalgia thrill, and apps can still achieve the same result by swapping the character explicitely.

from terminal.