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-rw-r--r--src/plugins/graphicssystems/meego/dithering.cpp147
1 files changed, 52 insertions, 95 deletions
diff --git a/src/plugins/graphicssystems/meego/dithering.cpp b/src/plugins/graphicssystems/meego/dithering.cpp
index 91e3337..2561c22 100644
--- a/src/plugins/graphicssystems/meego/dithering.cpp
+++ b/src/plugins/graphicssystems/meego/dithering.cpp
@@ -39,15 +39,22 @@
**
****************************************************************************/
-// This is an implementation of the 32bit => 16bit Floyd-Steinberg dithering.
+// Implements two dithering methods:
+//
+// * convertRGBA32_to_RGB565
+//
+// This is implemented using Ordered Bayer Dithering. The code has been adapted
+// from QX11PixmapData::fromImage. This method was originally implemented using
+// Floyd-Steinberg dithering but was later changed to Ordered Dithering because
+// of the better quality of the results.
+//
+// * convertRGBA32_to_RGBA4444
+//
+// This is implemented using Floyd-Steinberg dithering.
+//
// The alghorithm used here is not the fastest possible but it's prolly fast enough:
// uses look-up tables, integer-only arthmetics and works in one pass on two lines
// at a time. It's a high-quality dithering using 1/8 diffusion precission.
-// Two functions here to look at:
-//
-// * convertRGBA32_to_RGB565
-// * convertRGBA32_to_RGBA4444
-//
// Each channel (RGBA) is diffused independently and alpha is dithered too.
#include <string.h>
@@ -76,113 +83,63 @@
// Converts incoming RGB32 (QImage::Format_RGB32) to RGB565. Returns the newly allocated data.
unsigned short* convertRGB32_to_RGB565(const unsigned char *in, int width, int height, int stride)
{
+ static bool thresholdMapInitialized = false;
+ static int thresholdMap[16][16];
+
+ if (!thresholdMapInitialized) {
+ int i;
+ int j;
+ int n;
+
+ thresholdMap[0][0] = 0;
+ thresholdMap[1][0] = 2;
+ thresholdMap[0][1] = 3;
+ thresholdMap[1][1] = 1;
+
+ for (n=2; n<16; n*=2) {
+ for (i=0; i<n; i++) {
+ for (j=0; j<n; j++) {
+ thresholdMap[i][j] *= 4;
+ thresholdMap[i+n][j] = thresholdMap[i][j] + 2;
+ thresholdMap[i][j+n] = thresholdMap[i][j] + 3;
+ thresholdMap[i+n][j+n] = thresholdMap[i][j] + 1;
+ }
+ }
+ }
+
+ thresholdMapInitialized = true;
+ }
+
// Output line stride. Aligned to 4 bytes.
int alignedWidth = width;
if (alignedWidth % 2 > 0)
alignedWidth++;
// Will store output
- unsigned short *out = (unsigned short *) malloc(alignedWidth * height * 2);
-
- // Lookup tables for the 8bit => 6bit and 8bit => 5bit conversion
- unsigned char lookup_8bit_to_5bit[256];
- short lookup_8bit_to_5bit_diff[256];
- unsigned char lookup_8bit_to_6bit[256];
- short lookup_8bit_to_6bit_diff[256];
-
- // Macros for the conversion using the lookup table.
- #define CONVERT_8BIT_TO_5BIT(v) (lookup_8bit_to_5bit[v])
- #define DIFF_8BIT_TO_5BIT(v) (lookup_8bit_to_5bit_diff[v])
-
- #define CONVERT_8BIT_TO_6BIT(v) (lookup_8bit_to_6bit[v])
- #define DIFF_8BIT_TO_6BIT(v) (lookup_8bit_to_6bit_diff[v])
-
- int i;
- int x, y, c; // Pixel we're processing. c is component number (0, 1, 2 for r, b, b)
- short component[3]; // Stores the new components (r, g, b) for pixel produced during conversion
- short diff; // The difference between the converted value and the original one. To be accumulated.
- QVarLengthArray <short> accumulatorData(3 * width * 2); // Data for three acumulators for r, g, b. Each accumulator is two lines.
- short *accumulator[3]; // Helper for accessing the accumulator on a per-channel basis more easily.
- accumulator[0] = accumulatorData.data();
- accumulator[1] = accumulatorData.data() + width;
- accumulator[2] = accumulatorData.data() + (width * 2);
-
- // Produce the conversion lookup tables.
- for (i = 0; i < 256; i++) {
- lookup_8bit_to_5bit[i] = round(i / 8.0);
-
- // Before bitshifts: (i * 8) - (... * 8 * 8)
- lookup_8bit_to_5bit_diff[i] = (i << 3) - (lookup_8bit_to_5bit[i] << 6);
- if (lookup_8bit_to_5bit[i] > 31)
- lookup_8bit_to_5bit[i] -= 1;
-
- lookup_8bit_to_6bit[i] = round(i / 4.0);
-
- // Before bitshifts: (i * 8) - (... * 4 * 8)
- lookup_8bit_to_6bit_diff[i] = (i << 3) - (lookup_8bit_to_6bit[i] << 5);
- if (lookup_8bit_to_6bit[i] > 63)
- lookup_8bit_to_6bit[i] -= 1;
- }
+ unsigned short *out = (unsigned short *)malloc (alignedWidth * height * 2);
- // Clear the accumulators
- memset(accumulator[0], 0, width * 4);
- memset(accumulator[1], 0, width * 4);
- memset(accumulator[2], 0, width * 4);
+ int x;
+ int y;
+ int threshold;
// For each line...
for (y = 0; y < height; y++) {
- // For each accumulator, move the second line (index 1) to replace the first line (index 0).
- // Clear the second line (index 1)
- memcpy(accumulator[0], accumulator[0] + width, width * 2);
- memset(accumulator[0] + width, 0, width * 2);
-
- memcpy(accumulator[1], accumulator[1] + width, width * 2);
- memset(accumulator[1] + width, 0, width * 2);
-
- memcpy(accumulator[2], accumulator[2] + width, width * 2);
- memset(accumulator[2] + width, 0, width * 2);
-
// For each column....
for (x = 0; x < width; x++) {
- // For each component (r, g, b)...
- for (c = 0; c < 3; c++) {
+ int r = GET_RGBA_COMPONENT(in, x, y, stride, 0);
+ int g = GET_RGBA_COMPONENT(in, x, y, stride, 1);
+ int b = GET_RGBA_COMPONENT(in, x, y, stride, 2);
- // Get the 8bit value from the original image
- component[c] = GET_RGBA_COMPONENT(in, x, y, stride, c);
-
- // Add the diffusion for this pixel we stored in the accumulator.
- // >> 7 because the values in accumulator are stored * 128
- if (x != 0 && x != (width - 1)) {
- if (accumulator[c][x] >> 7 != 0)
- component[c] += rand() % accumulator[c][x] >> 7;
- }
-
- // Make sure we're not over the boundaries.
- CLAMP_256(component[c]);
-
- // For green component we use 6 bits. Otherwise 5 bits.
- // Store the difference from converting 8bit => 6 bit and the orig pixel.
- // Convert 8bit => 6(5) bit.
- if (c == 1) {
- diff = DIFF_8BIT_TO_6BIT(component[c]);
- component[c] = CONVERT_8BIT_TO_6BIT(component[c]);
- } else {
- diff = DIFF_8BIT_TO_5BIT(component[c]);
- component[c] = CONVERT_8BIT_TO_5BIT(component[c]);
- }
+ threshold = thresholdMap[x%16][y%16];
- // Distribute the difference according to the matrix in the
- // accumulation bufffer.
- ACCUMULATE(accumulator[c], x + 1, 0, width, diff * 3);
- ACCUMULATE(accumulator[c], x - 1, 1, width, diff * 5);
- ACCUMULATE(accumulator[c], x, 1, width, diff * 5);
- ACCUMULATE(accumulator[c], x + 1, 1, width, diff * 3);
- }
+ if (r <= (255-(1<<3)) && ((r<<5) & 255) > threshold) r += (1<<3);
+ if (g <= (255-(1<<2)) && ((g<<6) & 255) > threshold) g += (1<<2);
+ if (b <= (255-(1<<3)) && ((b<<5) & 255) > threshold) b += (1<<3);
// Write the newly produced pixel
- PUT_565(out, x, y, alignedWidth, component[2], component[1], component[0]);
+ PUT_565(out, x, y, alignedWidth, ((b >> 3) & 0x1f), ((g >> 2) & 0x3f), ((r >> 3) & 0x1f));
}
}