make efficient use of available display area

fix calculation of the text baselines, using getAscent() in favor of
getMaxCharHeight(), which includes ascent and descent. this moves the
first text up and allows to insert margin between the lines until the
display area is fully utilized.

on large displays, if the small diagram is selected, keep the first line
rather low to avoid collision with the diagram y-axis label. in this mode,
there is still more space between the text lines as before, allowing for
improved readability.

src/Display_Graphic.cpp

@@ -67,11 +67,19 @@ void DisplayGraphicClass::init(Scheduler& scheduler, const DisplayType_t type, c
 
 void DisplayGraphicClass::calcLineHeights()
 {
-    uint8_t yOff = 0;
+    bool diagram = (_isLarge && _diagram_mode == DiagramMode_t::Small);
+    // the diagram needs space. we need to keep
+    // away from the y-axis label in particular.
+    uint8_t yOff = (diagram?7:0);
     for (uint8_t i = 0; i < 4; i++) {
         setFont(i);
-        yOff += (_display->getMaxCharHeight());
+        yOff += _display->getAscent();
         _lineOffsets[i] = yOff;
+        yOff += ((!_isLarge || diagram)?2:3);
+        // the descent is a negative value and moves the *next* line's
+        // baseline. the first line never uses a letter with descent and
+        // we need that space when showing the small diagram.
+        yOff -= ((i == 0 && diagram)?0:_display->getDescent());
     }
 }
 

src/WebApi_device.cpp

@@ -166,12 +166,12 @@ void WebApiDeviceClass::onDeviceAdminPost(AsyncWebServerRequest* request)
         config.Led_Single[i].Brightness = min<uint8_t>(100, config.Led_Single[i].Brightness);
     }
 
+    Display.setDiagramMode(static_cast<DiagramMode_t>(config.Display.Diagram.Mode));
     Display.setOrientation(config.Display.Rotation);
     Display.enablePowerSafe = config.Display.PowerSafe;
     Display.enableScreensaver = config.Display.ScreenSaver;
     Display.setContrast(config.Display.Contrast);
     Display.setLanguage(config.Display.Language);
-    Display.setDiagramMode(static_cast<DiagramMode_t>(config.Display.Diagram.Mode));
     Display.Diagram().updatePeriod();
 
     WebApi.writeConfig(retMsg);

src/main.cpp

@@ -120,12 +120,12 @@ void setup()
         pin.display_clk,
         pin.display_cs,
         pin.display_reset);
+    Display.setDiagramMode(static_cast<DiagramMode_t>(config.Display.Diagram.Mode));
     Display.setOrientation(config.Display.Rotation);
     Display.enablePowerSafe = config.Display.PowerSafe;
     Display.enableScreensaver = config.Display.ScreenSaver;
     Display.setContrast(config.Display.Contrast);
     Display.setLanguage(config.Display.Language);
-    Display.setDiagramMode(static_cast<DiagramMode_t>(config.Display.Diagram.Mode));
     Display.setStartupDisplay();
     MessageOutput.println("done");