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Crosspoint/lib/Epub/Epub/converters/DirectPixelWriter.h
T

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C

#pragma once
#include <GfxRenderer.h>
#include <HalDisplay.h>
#include <stdint.h>
#include <cassert>
// Direct framebuffer writer that eliminates per-pixel overhead from the image
// rendering hot path. Pre-computes orientation transform as linear coefficients
// and caches render-mode state so the inner loop is: one multiply, one add,
// one shift, and one AND per pixel — no branches, no method calls.
//
// Caller is responsible for ensuring (outX, outY) are within screen bounds.
// ImageBlock::render() already validates this before entering the pixel loop,
// and the JPEG/PNG callbacks pre-clamp destination ranges to screen bounds.
struct DirectPixelWriter {
uint8_t* fb;
GfxRenderer::RenderMode mode;
uint16_t displayWidthBytes; // Runtime framebuffer stride (X4: 100, X3: 99)
// Active write target: for tiled grayscale, fb is the band scratch, originY is
// the band's top physical row, and clipRows is the band height. Off-band
// pixels are dropped. With no strip active these collapse to the full frame
// (originY 0, clipRows panelHeight) so the clip doubles as a bounds guard.
int originY;
int clipRows;
// Orientation is collapsed into a linear transform:
// phyX = phyXBase + x * phyXStepX + y * phyXStepY
// phyY = phyYBase + x * phyYStepX + y * phyYStepY
int phyXBase, phyYBase;
int phyXStepX, phyYStepX; // per logical-X step
int phyXStepY, phyYStepY; // per logical-Y step
// Row-precomputed: the Y-dependent portion of the physical coords
int rowPhyXBase, rowPhyYBase;
void init(GfxRenderer& renderer) {
fb = renderer.getWriteTarget();
originY = renderer.getWriteOriginY();
clipRows = renderer.getWriteRows();
mode = renderer.getRenderMode();
displayWidthBytes = renderer.getDisplayWidthBytes();
const int phyW = renderer.getDisplayWidth();
const int phyH = renderer.getDisplayHeight();
switch (renderer.getOrientation()) {
case GfxRenderer::Portrait:
// phyX = y, phyY = (phyH-1) - x
phyXBase = 0;
phyYBase = phyH - 1;
phyXStepX = 0;
phyYStepX = -1;
phyXStepY = 1;
phyYStepY = 0;
break;
case GfxRenderer::LandscapeClockwise:
// phyX = (phyW-1) - x, phyY = (phyH-1) - y
phyXBase = phyW - 1;
phyYBase = phyH - 1;
phyXStepX = -1;
phyYStepX = 0;
phyXStepY = 0;
phyYStepY = -1;
break;
case GfxRenderer::PortraitInverted:
// phyX = (phyW-1) - y, phyY = x
phyXBase = phyW - 1;
phyYBase = 0;
phyXStepX = 0;
phyYStepX = 1;
phyXStepY = -1;
phyYStepY = 0;
break;
case GfxRenderer::LandscapeCounterClockwise:
// phyX = x, phyY = y
phyXBase = 0;
phyYBase = 0;
phyXStepX = 1;
phyYStepX = 0;
phyXStepY = 0;
phyYStepY = 1;
break;
default:
// Fallback to LandscapeCounterClockwise (identity transform)
phyXBase = 0;
phyYBase = 0;
phyXStepX = 1;
phyYStepX = 0;
phyXStepY = 0;
phyYStepY = 1;
break;
}
}
// Call once per row before the column loop.
// Pre-computes the Y-dependent portion so writePixel() only needs the X part.
inline void beginRow(int logicalY) {
rowPhyXBase = phyXBase + logicalY * phyXStepY;
rowPhyYBase = phyYBase + logicalY * phyYStepY;
}
// For the current row (set via beginRow), narrow [colStart, colEnd) to the
// columns whose pixels fall inside the active strip band. writePixel() would
// clip the rest anyway, but on a strip pass that is most of a full-page image
// (only ~one strip-height worth of columns survive in portrait); skipping them
// here avoids the per-pixel unpack+transform entirely. For full-frame passes
// (clipRows == panel height) the range is unchanged. xBase is the logical X of
// column 0; the band test mirrors writePixel(): 0 <= phyY - originY < clipRows.
inline void bandColRange(int xBase, int width, int& colStart, int& colEnd) const {
// init() only ever sets phyYStepX to 0, +1, or -1; the +1/-1 solve below
// relies on that.
assert(phyYStepX == 0 || phyYStepX == 1 || phyYStepX == -1);
colStart = 0;
colEnd = width;
if (phyYStepX == 0) {
// phyY is constant across the row: the whole row is in-band or out.
const int sy = rowPhyYBase - originY;
if (static_cast<unsigned>(sy) >= static_cast<unsigned>(clipRows)) colEnd = 0;
return;
}
// phyY = rowPhyYBase + logicalX * phyYStepX (phyYStepX is +1 or -1).
// Solve originY <= phyY <= originY + clipRows - 1 for logicalX.
const int loY = originY;
const int hiY = originY + clipRows - 1;
int xLo, xHi;
if (phyYStepX > 0) {
xLo = loY - rowPhyYBase;
xHi = hiY - rowPhyYBase;
} else {
xLo = rowPhyYBase - hiY;
xHi = rowPhyYBase - loY;
}
const int cs = xLo - xBase;
const int ce = xHi - xBase + 1; // exclusive
if (cs > colStart) colStart = cs;
if (ce < colEnd) colEnd = ce;
if (colStart < 0) colStart = 0;
if (colEnd > width) colEnd = width;
if (colStart > colEnd) colStart = colEnd;
}
// Write a single 2-bit dithered pixel value to the framebuffer.
// Must be called after beginRow() for the current row.
// No bounds checking — caller guarantees coordinates are valid.
inline void writePixel(int logicalX, uint8_t pixelValue) const {
// Determine whether to draw based on render mode
bool draw;
bool state;
switch (mode) {
case GfxRenderer::BW:
draw = (pixelValue < 3);
state = true;
break;
case GfxRenderer::GRAYSCALE_MSB:
draw = (pixelValue == 1 || pixelValue == 2);
state = false;
break;
case GfxRenderer::GRAYSCALE_LSB:
draw = (pixelValue == 1);
state = false;
break;
default:
return;
}
if (!draw) return;
const int phyX = rowPhyXBase + logicalX * phyXStepX;
const int phyY = rowPhyYBase + logicalX * phyYStepX;
// Band-local row. The unsigned compare drops both off-band pixels (strip
// mode) and any out-of-frame row (full-frame mode) in one branch.
const int sy = phyY - originY;
if (static_cast<unsigned>(sy) >= static_cast<unsigned>(clipRows)) return;
const uint16_t byteIndex = static_cast<uint16_t>(sy * displayWidthBytes + (phyX >> 3));
const uint8_t bitMask = 1 << (7 - (phyX & 7));
if (state) {
fb[byteIndex] &= ~bitMask; // Clear bit (draw black)
} else {
fb[byteIndex] |= bitMask; // Set bit (draw white)
}
}
};
// Direct cache writer that eliminates per-pixel overhead from PixelCache::setPixel().
// Pre-computes row pointer so the inner loop is just byte index + bit manipulation.
//
// The cache buffer is a small streaming band (e.g. 16 rows), not the full image,
// so a band-relative row/column that lands outside it would corrupt adjacent
// heap. This writer therefore bounds-checks every access: beginRow() invalidates
// the row when it falls outside the band, and writePixel() drops out-of-range
// columns. This path only runs during the single decode that populates the
// cache, never on the screen render hot path, so the checks are cheap.
struct DirectCacheWriter {
uint8_t* buffer;
int bytesPerRow;
int bandRows;
int originX;
uint8_t* rowPtr; // Pre-computed for current row; nullptr if row is out of band
void init(uint8_t* cacheBuffer, int cacheBytesPerRow, int cacheBandRows, int cacheOriginX) {
buffer = cacheBuffer;
bytesPerRow = cacheBytesPerRow;
bandRows = cacheBandRows;
originX = cacheOriginX;
rowPtr = nullptr;
}
// Call once per row before the column loop. Drops rows outside the band.
inline void beginRow(int screenY, int cacheOriginY) {
const int localRow = screenY - cacheOriginY;
rowPtr = (static_cast<unsigned>(localRow) < static_cast<unsigned>(bandRows))
? buffer + (size_t)localRow * bytesPerRow
: nullptr;
}
// Write a 2-bit pixel value. Drops the write if the row is out of band or the
// column is out of range.
inline void writePixel(int screenX, uint8_t value) const {
if (!rowPtr) return;
const int localX = screenX - originX;
const int byteIdx = localX >> 2; // localX / 4
if (static_cast<unsigned>(byteIdx) >= static_cast<unsigned>(bytesPerRow)) return;
const int bitShift = 6 - (localX & 3) * 2; // MSB first: pixel 0 at bits 6-7
rowPtr[byteIdx] = (rowPtr[byteIdx] & ~(0x03 << bitShift)) | ((value & 0x03) << bitShift);
}
};