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Optimisation of Bitmap parsing

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Dave Allie 2025-12-19 00:21:51 +11:00
parent f72d2c372c
commit 06bb39e03a
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GPG Key ID: F2FDDB3AD8D0276F
3 changed files with 66 additions and 78 deletions
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125
lib/GfxRenderer/Bitmap.cpp
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@ -99,18 +99,15 @@ BmpReaderError Bitmap::parseHeaders() {
if (width <= 0 || height <= 0) return BmpReaderError::BadDimensions; if (width <= 0 || height <= 0) return BmpReaderError::BadDimensions;
// Palette for 8-bit indexed images // Pre-calculate Row Bytes to avoid doing this every row
for (int i = 0; i < 256; i++) paletteLum[i] = static_cast<uint8_t>(i); // default grayscale ramp rowBytes = (width * bpp + 31) / 32 * 4;
for (int i = 0; i < 256; i++) paletteLum[i] = static_cast<uint8_t>(i);
if (colorsUsed > 0) { if (colorsUsed > 0) {
for (uint32_t i = 0; i < colorsUsed; i++) { for (uint32_t i = 0; i < colorsUsed; i++) {
const int b = file.read(); uint8_t rgb[4];
const int g = file.read(); file.read(rgb, 4); // Read B, G, R, Reserved in one go
const int r = file.read(); paletteLum[i] = (77u * rgb[2] + 150u * rgb[1] + 29u * rgb[0]) >> 8;
file.seek(1, SeekCur); // reserved
const auto bb = static_cast<uint8_t>(b < 0 ? 0 : b);
const auto gg = static_cast<uint8_t>(g < 0 ? 0 : g);
const auto rr = static_cast<uint8_t>(r < 0 ? 0 : r);
paletteLum[i] = static_cast<uint8_t>((77u * rr + 150u * gg + 29u * bb) >> 8);
} }
} }
@ -122,72 +119,64 @@ BmpReaderError Bitmap::parseHeaders() {
} }
// packed 2bpp output, 0 = black, 1 = dark gray, 2 = light gray, 3 = white // packed 2bpp output, 0 = black, 1 = dark gray, 2 = light gray, 3 = white
BmpReaderError Bitmap::readRow(uint8_t* data, const size_t dataLen, size_t* read) const { BmpReaderError Bitmap::readRow(uint8_t* data, uint8_t* rowBuffer) const {
// Validate data is long enough to hold a row worth of data // Note: rowBuffer should be pre-allocated by the caller to size 'rowBytes'
const size_t outputBytes = (width + 3) / 4; if (file.read(rowBuffer, rowBytes) != rowBytes) return BmpReaderError::ShortReadRow;
if (dataLen < outputBytes) {
*read = 0;
return BmpReaderError::BufferTooSmall;
}
// setup data to be all black uint8_t* outPtr = data;
memset(data, 0x00, outputBytes); uint8_t currentOutByte = 0;
int bitShift = 6;
const size_t rowBytes = (width * bpp + 31) / 32 * 4; // Helper lambda to pack 2bpp color into the output stream
const auto rowBuffer = static_cast<uint8_t*>(malloc(rowBytes)); auto packPixel = [&](uint8_t lum) {
if (!rowBuffer) { uint8_t color = (lum >> 6); // Simple 2-bit reduction: 0-255 -> 0-3
*read = 0; currentOutByte |= (color << bitShift);
return BmpReaderError::OomRowBuffer; if (bitShift == 0) {
} *outPtr++ = currentOutByte;
currentOutByte = 0;
if (file.read(rowBuffer, rowBytes) != rowBytes) { bitShift = 6;
free(rowBuffer);
*read = 0;
return BmpReaderError::ShortReadRow;
}
for (int bmpX = 0; bmpX < width; bmpX++) {
uint8_t lum;
if (bpp == 1) {
const uint8_t byte = rowBuffer[bmpX / 8];
const uint8_t bit = 7 - (bmpX % 8);
const bool bitSet = (byte >> bit) & 0x01;
// In 1bpp BMPs, palette index 0 is conventionally black and index 1 is white.
lum = bitSet ? 0xFF : 0x00;
} else if (bpp == 2) {
const uint8_t byte = rowBuffer[bmpX / 4];
const uint8_t twobit = 6 - ((bmpX * 2) % 8);
const uint8_t val = (byte >> twobit) & 0x3;
lum = paletteLum[val];
} else if (bpp == 8) {
const uint8_t idx = rowBuffer[bmpX];
lum = paletteLum[idx];
} else { } else {
// 24 / 32 bitShift -= 2;
const uint8_t* px = &rowBuffer[bmpX * bpp / 8];
const uint8_t b = px[0];
const uint8_t g = px[1];
const uint8_t r = px[2];
lum = static_cast<uint8_t>((77u * r + 150u * g + 29u * b) >> 8);
} }
};
uint8_t color; switch (bpp) {
if (lum >= 192) { case 8: {
color = 0x3; // white for (int x = 0; x < width; x++) {
} else if (lum >= 128) { packPixel(paletteLum[rowBuffer[x]]);
color = 0x2; // light gray }
} else if (lum >= 64) { break;
color = 0x1; // dark gray }
} else { case 24: {
color = 0x0; // black const uint8_t* p = rowBuffer;
for (int x = 0; x < width; x++) {
uint8_t lum = (77u * p[2] + 150u * p[1] + 29u * p[0]) >> 8;
packPixel(lum);
p += 3;
}
break;
}
case 1: {
for (int x = 0; x < width; x++) {
uint8_t lum = (rowBuffer[x >> 3] & (0x80 >> (x & 7))) ? 0xFF : 0x00;
packPixel(lum);
}
break;
}
case 32: {
const uint8_t* p = rowBuffer;
for (int x = 0; x < width; x++) {
uint8_t lum = (77u * p[2] + 150u * p[1] + 29u * p[0]) >> 8;
packPixel(lum);
p += 4;
}
break;
} }
data[bmpX / 4] |= (color << (6 - ((bmpX % 4) * 2)));
} }
free(rowBuffer); // Flush remaining bits if width is not a multiple of 4
*read = outputBytes; if (bitShift != 6) *outPtr = currentOutByte;
return BmpReaderError::Ok; return BmpReaderError::Ok;
} }

6
lib/GfxRenderer/Bitmap.h
View File

@ -27,14 +27,15 @@ class Bitmap {
public: public:
static const char* errorToString(BmpReaderError err); static const char* errorToString(BmpReaderError err);
explicit Bitmap(File& file) : file(file) {}; explicit Bitmap(File& file) : file(file) {}
BmpReaderError parseHeaders(); BmpReaderError parseHeaders();
BmpReaderError readRow(uint8_t* data, size_t dataLen, size_t* read) const; BmpReaderError readRow(uint8_t* data, uint8_t* rowBuffer) const;
BmpReaderError rewindToData() const; BmpReaderError rewindToData() const;
int getWidth() const { return width; } int getWidth() const { return width; }
int getHeight() const { return height; } int getHeight() const { return height; }
bool isTopDown() const { return topDown; } bool isTopDown() const { return topDown; }
bool hasGreyscale() const { return bpp > 1; } bool hasGreyscale() const { return bpp > 1; }
int getRowBytes() const { return rowBytes; }
private: private:
static uint16_t readLE16(File& f); static uint16_t readLE16(File& f);
@ -46,5 +47,6 @@ class Bitmap {
bool topDown = false; bool topDown = false;
uint32_t bfOffBits = 0; uint32_t bfOffBits = 0;
uint16_t bpp = 0; uint16_t bpp = 0;
int rowBytes = 0;
uint8_t paletteLum[256] = {}; uint8_t paletteLum[256] = {};
}; };

13
lib/GfxRenderer/GfxRenderer.cpp
View File

@ -134,6 +134,7 @@ void GfxRenderer::drawBitmap(const Bitmap& bitmap, const int x, const int y, con
const uint8_t outputRowSize = (bitmap.getWidth() + 3) / 4; const uint8_t outputRowSize = (bitmap.getWidth() + 3) / 4;
auto* outputRow = static_cast<uint8_t*>(malloc(outputRowSize)); auto* outputRow = static_cast<uint8_t*>(malloc(outputRowSize));
auto* rowBytes = static_cast<uint8_t*>(malloc(bitmap.getRowBytes()));
for (int bmpY = 0; bmpY < bitmap.getHeight(); bmpY++) { for (int bmpY = 0; bmpY < bitmap.getHeight(); bmpY++) {
// The BMP's (0, 0) is the bottom-left corner (if the height is positive, top-left if negative). // The BMP's (0, 0) is the bottom-left corner (if the height is positive, top-left if negative).
@ -146,18 +147,13 @@ void GfxRenderer::drawBitmap(const Bitmap& bitmap, const int x, const int y, con
break; break;
} }
size_t readBytes; if (bitmap.readRow(outputRow, rowBytes) != BmpReaderError::Ok) {
if (bitmap.readRow(outputRow, outputRowSize, &readBytes) != BmpReaderError::Ok) { Serial.printf("[%lu] [GFX] Failed to read row %d from bitmap\n", millis(), bmpY);
free(outputRow); free(outputRow);
free(rowBytes);
return; return;
} }
if (readBytes != outputRowSize) {
Serial.printf("[%lu] [GFX] Failed to read BMP row data, got: %d, expected: %d\n", millis(), readBytes,
outputRowSize);
break;
}
for (int bmpX = 0; bmpX < bitmap.getWidth(); bmpX++) { for (int bmpX = 0; bmpX < bitmap.getWidth(); bmpX++) {
int screenX = x + bmpX; int screenX = x + bmpX;
if (isScaled) { if (isScaled) {
@ -180,6 +176,7 @@ void GfxRenderer::drawBitmap(const Bitmap& bitmap, const int x, const int y, con
} }
free(outputRow); free(outputRow);
free(rowBytes);
} }
void GfxRenderer::clearScreen(const uint8_t color) const { einkDisplay.clearScreen(color); } void GfxRenderer::clearScreen(const uint8_t color) const { einkDisplay.clearScreen(color); }