From 8445e04bae016b6bd74705902972e66ae7fe37c1 Mon Sep 17 00:00:00 2001
From: "sgunderson@bigfoot.com" <>
Date: Sun, 31 May 2009 18:35:08 +0200
Subject: [PATCH] In the driver, store the image data and output one of the
 components as a PGM file.

---
 driver.c | 66 ++++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 45 insertions(+), 21 deletions(-)

diff --git a/driver.c b/driver.c
index 2e5bda6..06d94d9 100644
--- a/driver.c
+++ b/driver.c
@@ -14,8 +14,11 @@ struct jpeg_image {
 	unsigned width, height;
 	unsigned num_components;
 	unsigned hsample[256], vsample[256], qtable[256];
+	unsigned max_hsample, max_vsample;
+	unsigned num_blocks_horizontal, num_blocks_vertical;
 	uint32_t qvalues[256][DCTSIZE2];
 	void* idct_data[256];
+	uint8_t* pixel_data[256];
 };
 
 ssize_t stdio_read(void* userdata, uint8_t* buf, size_t count) 
@@ -79,9 +82,32 @@ void read_sof(struct byte_source* source, struct jpeg_image* image)
 		image->qtable[c] = read_uint8(byte_source_input_func, source);
 		len -= 3;
 
+		if (image->hsample[c] > image->max_hsample) {
+			image->max_hsample = image->hsample[c];
+		}
+		if (image->vsample[c] > image->max_vsample) {
+			image->max_vsample = image->vsample[c];
+		}
+
 		fprintf(stderr, "Component %u: sampling factors %u x %x, quantization table %u\n",
 			c, image->hsample[c], image->vsample[c], image->qtable[c]);
 	}
+	
+	image->num_blocks_horizontal = (image->width + image->max_hsample * DCTSIZE - 1) / (image->max_hsample * DCTSIZE);
+	image->num_blocks_vertical = (image->height + image->max_vsample * DCTSIZE - 1) / (image->max_vsample * DCTSIZE);
+
+	for (unsigned c = 0; c < 256; ++c) {
+		if (image->hsample[c] == 0) {
+			continue;
+		}
+
+		unsigned width = image->num_blocks_horizontal * image->hsample[c] * DCTSIZE;
+		unsigned height = image->num_blocks_vertical * image->vsample[c] * DCTSIZE;
+		image->pixel_data[c] = (uint8_t*)malloc(width * height);
+		assert(image->pixel_data[c] != NULL);
+
+		fprintf(stderr, "Component %u: allocating %d x %d\n", c, width, height);
+	}
 }
 
 void read_scan(struct byte_source* source, struct jpeg_image* image, huffman_tables_t* tables)
@@ -123,16 +149,12 @@ void read_scan(struct byte_source* source, struct jpeg_image* image, huffman_tab
 	struct bit_source bits;
 	init_bit_source(&bits, byte_source_input_func, source);
 		
-	// Some debugging code.
-	assert(image->width % 8 == 0);
-	int y_stride = image->width;
-	uint8_t* y_row_data = (uint8_t*)malloc(y_stride * DCTSIZE * image->vsample[1]);
-	assert(y_row_data != NULL);
-	int xb = 0;
+	unsigned mcu_x = 0, mcu_y = 0;
 
 	for ( ;; ) {
 		for (unsigned c = 0; c < num_components; ++c) {
 			unsigned cn = component_num[c];
+			unsigned stride = image->num_blocks_horizontal * image->hsample[cn] * DCTSIZE;
 			assert(image->idct_data[image->qtable[cn]] != NULL);
 			
 			for (unsigned local_yb = 0; local_yb < image->vsample[cn]; ++local_yb) {
@@ -172,26 +194,28 @@ void read_scan(struct byte_source* source, struct jpeg_image* image, huffman_tab
 					uint8_t pixdata[DCTSIZE2];	
 					idct_choice(coeff, image->idct_data[image->qtable[cn]], pixdata);
 
-					if (cn != 1) {
-						continue;
-					}
-
-					for (int y = 0; y < DCTSIZE; ++y) {
-						memcpy(y_row_data + (local_yb * DCTSIZE + y) * y_stride + (xb + local_xb) * DCTSIZE,
+					for (unsigned y = 0; y < DCTSIZE; ++y) {
+						unsigned real_x = (mcu_x * image->hsample[cn] + local_xb) * DCTSIZE;
+						unsigned real_y = (mcu_y * image->vsample[cn] + local_yb) * DCTSIZE + y;
+					
+						memcpy(image->pixel_data[cn] + real_y * stride + real_x,
 						       pixdata + y * DCTSIZE,
 						       DCTSIZE);
 					}
 				}
 			}
-
-			if (cn != 1) {
-				continue;
-			}
-
-			xb += image->hsample[cn];
-			if (xb * DCTSIZE == y_stride) {
-				fwrite(y_row_data, y_stride * DCTSIZE * image->vsample[cn], 1, stdout);
-				xb = 0;
+		}
+		
+		if (++mcu_x == image->num_blocks_horizontal) {
+			++mcu_y;
+			mcu_x = 0;
+
+			// Some debug code.
+			const int c = 1;
+			if (mcu_y == image->num_blocks_vertical) {
+				unsigned stride = image->num_blocks_horizontal * image->hsample[c] * DCTSIZE;
+				printf("P5\n%u %u\n255\n", stride, image->height);
+				fwrite(image->pixel_data[c], stride * image->height, 1, stdout);
 			}
 		}
 	}
-- 
2.39.2