diff options
Diffstat (limited to 'src/plugins/graphicssystems/meego/dithering.cpp')
| -rw-r--r-- | src/plugins/graphicssystems/meego/dithering.cpp | 147 |
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)); } } |