Alpha in background - help me understand

[royfalk]

Here's a code that repeats in many places (vdu.cpp:1005):

    const float background_alpha = configuration().graphics.hud.text_background_alpha_flt;  // 0.065
    GFXColor tpbg(tp->background_color);  // Store the original background color
    bool automatte = (0 == tpbg.a);  // If alpha is 0
    if (automatte) {
        GFXColor temp_background_color( 0, 0, 0, background_alpha );    // background color is now (0,0,0,16)
        tp->background_color = static_cast<ImU32>(temp_background_color);
    }
    tp->Draw(MangleString(retval,
                    _Universe->AccessCamera()->GetNebula() != NULL ? .4 : 0),
            scrolloffset,
            true,
            false,
            automatte);
    tp->background_color = static_cast<ImU32>(tpbg);  // Revert background color

Then, in hud.cpp, the Draw function did this (I got rid of this nonsense):

bool drawbg = (bgcol.a != 0);

// Draw the text background for this row
if (!automatte && drawbg) {
        GFXColorf(this->bgcol);
        DrawSquare(col, this->myDims.i, row - rowheight * .25, row + rowheight);
}

//always true <= **REALLY NOT. WHY IS THIS COMMENT HERE????**
// Draw a shadow?!
            if (automatte) {
                GFXColorf(this->bgcol);
                DrawSquare(col - origcol,
                        col - origcol + shadowlen / scalex,
                        -rowheight * .25 / scaley,
                        rowheight * .75 / scaley);
                GFXColorf(currentCol);
            }

// Another shadow ?
if (automatte) {
                GFXColorf(this->bgcol);
                DrawSquare(col - origcol,
                        col - origcol + shadowlen * 5 / (.5 * g_game.x_resolution),
                        -rowheight * .25 / scaley,
                        rowheight * .75 / scaley);
                GFXColorf(currentCol);
            }

// Draw background for the next lines
if (!automatte && drawbg) {
                GFXColorf(this->bgcol);
                DrawSquare(col, this->myDims.i, row - rowheight * .25, row + rowheight * .75);
            }

In short, two scenarios.
Scenario 1

1. alpha == 0
2. automatte
3. bg color = (0,0,0,16) very transparent black
4. Don't draw background. Draw shadows

Scenario 2

1. alpha != 0
2. !automatte
3. bg color = whatever
4. Draw background. Don't draw shadows

Did I get it right??

[stephengtuggy]

Wow, that's very weird. And hard to follow. You may have gotten it right? I'm not sure.