Fix large blacklevel step. Lower 25% of shades are now accessible.

There is a large step in brightness from level zero to level one.
After experimenting with various ST7789 options, I found that
decreasing VDV to 0x10 (-0.4V) fixes this issue.

The gamma change reduced the average error in brightness, but with the
underlying issue fixed, the gamma change has been reverted.

1 files changed, 6 insertions, 4 deletions

diff --git a/src/drivers/St7789.cpp b/src/drivers/St7789.cpp
index d520199e..3ed1beb4 100644
--- a/src/drivers/St7789.cpp
+++ b/src/drivers/St7789.cpp
@@ -23,7 +23,7 @@ void St7789::Init() {
   RowAddressSet();
   DisplayInversionOn();
   NormalModeOn();
-  SetGamma();
+  SetVdv();
   DisplayOn();
 }
 
@@ -115,9 +115,11 @@ void St7789::WriteToRam() {
   WriteCommand(static_cast<uint8_t>(Commands::WriteToRam));
 }
 
-void St7789::SetGamma() {
-  WriteCommand(static_cast<uint8_t>(Commands::GammaSet));
-  WriteData(0x04);
+void St7789::SetVdv() {
+  // By default there is a large step from pixel brightness zero to one.
+  // After experimenting with VCOMS, VRH and VDV, this was found to produce good results.
+  WriteCommand(static_cast<uint8_t>(Commands::VdvSet));
+  WriteData(0x10);
 }
 
 void St7789::DisplayOff() {