Practical EVE Bitmap Formats: PALETTED8, TEXTVGA, TEXT8X8 and BARGRAPH

Five EVE Screen Editor (ESE) demonstrations for FT810–FT813 and BT815–BT818.

Reference projects: BT815, 480 × 272, from ese-usecases-Paletted8-TextVGA-Text8x8-BarGraph.zip. These examples use synthetic demonstration data rather than measurements from connected instruments. The supplied projects were not independently run on FT81x hardware for this article.

1. Overview and source projects

Unlike ordinary pixel-colour textures, these formats store compact representations that the EVE graphics engine expands during display-list rendering. PALETTED8 holds colour indices; TEXTVGA holds a character/attribute pair per cell; TEXT8X8 holds one character per cell; BARGRAPH holds a height threshold per column.

Each example contains an .ese project, raw RAM_G payloads in resources/, and an overview screenshot. Open a project in EVE Screen Editor, configure BT815 / 480 × 272, and inspect its Content and Coprocessor tabs. The .raw resources are byte-exact memory images: firmware must place them at the corresponding RAM_G addresses before drawing.

2. PALETTED8 — thermal-camera image and palette-only alarm

The thermal demo quantizes a synthetic 160 × 120 temperature field to 19,200 byte indices. A separate 256-entry, four-byte-per-entry palette maps indices into colours, allowing colour mapping to change independently of the input pixels.

On these devices a coloured PALETTED8 bitmap is composed using four draws. COLOR_MASK enables one output channel at a time, and PALETTE_SOURCE selects the appropriate palette byte: 3 for A, 2 for R, 1 for G and 0 for B.

BEGIN(BITMAPS);
BITMAP_HANDLE(0);
BITMAP_SOURCE(1024);
BITMAP_LAYOUT(PALETTED8, 160, 120);
BITMAP_SIZE(BILINEAR, BORDER, BORDER, 320, 240);
BITMAP_TRANSFORM_A(0, 128);  /* BT81x 2x */
BITMAP_TRANSFORM_E(0, 128);
BLEND_FUNC(ONE, ZERO);
COLOR_MASK(0,0,0,1); PALETTE_SOURCE(3); VERTEX2II(8,20,0,0);
COLOR_MASK(1,0,0,0); PALETTE_SOURCE(2); VERTEX2II(8,20,0,0);
COLOR_MASK(0,1,0,0); PALETTE_SOURCE(1); VERTEX2II(8,20,0,0);
COLOR_MASK(0,0,1,0); PALETTE_SOURCE(0); VERTEX2II(8,20,0,0);
COLOR_MASK(1,1,1,1);
BLEND_FUNC(SRC_ALPHA,ONE_MINUS_SRC_ALPHA);

In UC_Paletted8_Thermal_Alarm, the 19,200-byte frame is unchanged. Only the palette and labels change: entries 181–255 (the configured 55 °C threshold and higher) are mapped to green RGB(0,255,64). Updating 75 palette entries costs just 300 bytes; replacing the complete palette costs 1,024 bytes.

Use case: false-colour temperature maps, heatmaps, alarm isotherms and themes. Trade-off: four full-image passes may increase worst-scanline rendering time.

3. TEXTVGA — a 2 KB CNC controller console

The console renders 60 columns × 17 rows of 8 × 16-pixel cells, filling the 480 × 272 display. Each cell is two bytes: a CP437 character followed by a VGA foreground/background attribute. The memory requirement is 60 × 17 × 2 = 2,040 bytes.

CLEAR(1,1,1);
BLEND_FUNC(ONE,ZERO);
BEGIN(BITMAPS);
BITMAP_HANDLE(0);
BITMAP_SOURCE(0);
BITMAP_LAYOUT(TEXTVGA,120,17);  /* 60 cells x 2 bytes */
BITMAP_SIZE(NEAREST,BORDER,BORDER,480,272);
VERTEX2II(0,0,0,0);

The attribute byte is ((background & 15) << 4) | (foreground & 15). Address an arbitrary cell with base + 2 * (row * 60 + column); updating a character or its colour requires only two bytes. The example includes CP437 borders, coloured selections and status readouts. Its explicit BLEND_FUNC(ONE,ZERO) preserves the intended opaque console background.

Use case: operator panels, service screens, industrial terminal emulation. Trade-off: fixed 8 × 16 cells and CP437 character repertoire.

4. TEXT8X8 — a scrolling CAN diagnostic trace

The CAN logger uses a 64-row × 64-column byte ring (4,096 bytes), plus 145 bytes for fixed headings and footer. Each byte identifies one 8 × 8 CP437 glyph; the colour is selected per draw with COLOR_RGB, not stored per cell.

For the example head position 10, the 30 visible rows are physical rows 44–63 and then 0–9. Rather than moving 30 rows of text, the display list selects the circular start with an 8.8 fixed-point vertical transform:

BITMAP_HANDLE(0);
BITMAP_SOURCE(0);
BITMAP_LAYOUT(TEXT8X8,64,64);
BITMAP_SIZE(NEAREST,REPEAT,REPEAT,480,240);
BITMAP_TRANSFORM_F(90112); /* 44 rows x 8 px x 256 */
COLOR_RGB(60,230,110);
VERTEX2II(0,24,0,0);

When a new message arrives, the MCU writes a 64-byte row, advances the head and adjusts the transform. For error highlighting, draw the same TEXT8X8 bitmap again, clipped to one 8-pixel-high row, with a different COLOR_RGB.

SCISSOR_XY(0,72);
SCISSOR_SIZE(480,8);
COLOR_RGB(255,70,60);
VERTEX2II(0,24,0,0);
SCISSOR_XY(0,0);
SCISSOR_SIZE(480,272);

Use case: CAN, UART and diagnostic logs. Trade-off: per-row highlighting requires updating scissor positions as the ring view scrolls.

5. BARGRAPH — 31-band spectrum with history

BARGRAPH stores a threshold byte per horizontal column. In the supplied example, a source row is painted where its source y exceeds the byte. A height h is encoded as 255 - h; byte 255 is empty. A 31-band spectrum uses 12 columns per band and a 2-column gap: 31 × 14 = 434 bytes. A separate 512-byte ring stores the scrolling history; labels add 159 bytes.

BITMAP_HANDLE(0);
BITMAP_SOURCE(0);
BITMAP_LAYOUT(BARGRAPH,434,1);
BITMAP_SIZE(NEAREST,BORDER,BORDER,434,150);
BITMAP_TRANSFORM_F(27136); /* (256-150) * 256 */

SCISSOR_XY(0,24); SCISSOR_SIZE(480,15);
COLOR_RGB(255,60,50); VERTEX2II(44,24,0,0);
SCISSOR_XY(0,39); SCISSOR_SIZE(480,30);
COLOR_RGB(255,200,0); VERTEX2II(44,24,0,0);
SCISSOR_XY(0,69); SCISSOR_SIZE(480,105);
COLOR_RGB(40,220,90); VERTEX2II(44,24,0,0);
SCISSOR_XY(0,0); SCISSOR_SIZE(480,272);

Drawing the same bitmap through three scissor bands creates red, yellow and green regions. Peak-hold markers are separate rectangles. Updating spectrum amplitude requires only the column bytes; scrolling history uses horizontal REPEAT and an x transform, avoiding a history-buffer copy. The example sets BITMAP_TRANSFORM_C(76800) for history column 300 and BITMAP_TRANSFORM_F(50176) for the 60-pixel-height history region.

Use case: VU meters, audio bands, trend displays and telemetry. Trade-off: source vertical coordinate space is 256 rows; taller visualizations need scaling or alternative rendering.

6. Compatibility, porting and practical checks

The supplied projects were generated for BT815. Their generator supports FT810, FT811, FT812, FT813, BT815, BT816, BT817 and BT818. On FT81x, the relevant 2× transform takes the one-argument 8.8 fixed-point syntax:

/* BT81x: precision argument and value */
BITMAP_TRANSFORM_A(0,128);
BITMAP_TRANSFORM_E(0,128);
/* FT81x: 8.8 signed fixed-point value */
BITMAP_TRANSFORM_A(128);
BITMAP_TRANSFORM_E(128);

python -m pip install numpy
python make_assets.py --device FT813
python make_assets.py --device BT817

For 800 × 480 ports, use VERTEX2F where x/y exceed VERTEX2II's 9-bit coordinates; use BITMAP_SIZE_H and BITMAP_LAYOUT_H where dimension and stride fields exceed their base-command limits. Reset persistent high-bit bitmap state when reusing handles. Verify RAM_G placement, the display-list swap and scanline timing on target hardware.

7. References

• Source: ese-usecases-Paletted8-TextVGA-Text8x8-BarGraph.zip supplied for this tutorial; see its README.md, make_assets.py, five .ese projects and resources/ assets.
• Bridgetek product and documentation portal
• Bridgetek open-source documentation
• EVE-MCU-Dev