External latin font (from font converter) shows discoloration

jhgorse · Oct 26th 2015, 9:05pm

I am seeing some discoloration of externally generated latin fonts in a horizontal band through the middle of the screen. The black text appears red-ish in the band. See the attached images.

The latin fonts were converted with 4bpp anti-aliasing while the Japanese font was not.

These red bands do not appear when using the default emWin latin fonts.

Any thoughts as to what may be causing this?

jhgorse · Oct 28th 2015, 8:00pm

I never debugged the entire issue. I disabled antialiasing on the font conversion and the red bands have disappeared. I assume it had something to do with the blending which was occurring.

SEGGER - Jörg · Oct 29th 2015, 10:04am

Hi,

Drawing AA-fonts requires the ability to read the content of the frame buffer to be able to mix the current content with the text color. How that reading operation works depends on the kind of the used display driver. Drivers with a direct interface like GUIDRV_Lin access the RAM by data- and address bus. Drivers with indirect interface like GUIDRV_FlexColor require reading functions passed by the structure GUI_PORT_API when calling GUIDRV_FlexColor_SetFunc().

Our assumption is that reading the frame buffer does not work right. Here is a small test which checks if reading basically works:

C Source Code

#include "GUI.h"
void _Test(void) {
const int dx = 50;
const int dy = 50;
const GUI_COLOR aColor[] = { GUI_RED, GUI_GREEN, GUI_BLUE };
const char * apText[] = {
"Red", "Green", "Blue"
};
GUI_RECT Rect = { 0, 0, dx - 1, dy - 1 };
int i;
GUI_SetTextMode(GUI_TM_TRANS);
for (i = 0; i < GUI_COUNTOF(aColor); i++) {
GUI_SetColor(aColor[i]);
GUI_FillRectEx(&Rect);
GUI_SetColor(GUI_WHITE);
GUI_DispStringInRect(apText[i], &Rect, GUI_TA_HCENTER | GUI_TA_VCENTER);
GUI_MoveRect(&Rect, dx, dy);
}
GUI_MoveRect(&Rect, -dx, -dy);
GUI_InvertRect(dx / 4, dy / 4, Rect.x1 - dx / 4, Rect.y1 - dy / 4);
GUI_MoveRect(&Rect, -dx, -dy);
GUI_InvertRect(Rect.x0, Rect.y0, Rect.x1, Rect.y1);
}
void MainTask(void) {
GUI_Init();
_Test();
while(1) {
GUI_Delay(100);
}
}

Display All

It should produce the attached screen.

It would be helpful to know if that works.

Regards, Jörg

jhgorse · Nov 9th 2015, 9:09pm

Jörg,

I have run the test pattern. It appears as expected.

I suspect it had to do with anti-aliasing or the memory-mapped lcd driver. In any case, using non anti-aliased fonts seems to be working.

Cheers,
Joe

asafbit · Nov 12th 2015, 12:58pm

please do the next test:

int i = 0;
while i<0xffffff
{
GUI_SetBkColor(i);
i+=0x010101;
GUI_Clear();
GUI_Delay(10);
}

that should draw black screen fade into white screen.

share the results please

SEGGER - Jörg · Jan 19th 2016, 12:40pm

Hi,

The test works (of course) without problems and fades from black to white.

Regards, Jörg

C Source Code

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