Add palette <-> PNG conversion.

Factored out from the existing PNG conversion functions. Part of #2.

src/GNUmakefile

@@ -59,6 +59,7 @@ OBJS =                      \
     pager/pager.o           \
     pager/plaintext.o       \
     palette/doom.o          \
+    palette/palette.o       \
     palette/palfs.o         \
     textures/actions.o      \
     textures/bundle.o       \

src/palette/doom.c

@@ -12,6 +12,7 @@
 #include <stdint.h>
 #include <string.h>
 
+#include "fs/vfile.h"
 #include "palette/palette.h"
 
 // TODO: Get palette from current WADs

src/palette/palette.c

@@ -0,0 +1,122 @@
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "common.h"
+#include "fs/vfile.h"
+#include "palette/palette.h"
+#include "conv/graphic.h"
+#include "conv/error.h"
+#include "conv/vpng.h"
+
+#define PALETTE_SIZE   (256 * 3)
+
+struct palette_set *PAL_FromImageFile(VFILE *input)
+{
+	struct png_context ctx;
+	int bit_depth, color_type, ilace_type, comp_type, filter_method;
+	int rowstep, x, y, num_palettes;
+	png_uint_32 width, height;
+	uint8_t *rowbuf;
+	struct palette_set *result = NULL;
+
+	if (!V_OpenPNGRead(&ctx, input)) {
+		return NULL;
+	}
+
+	png_read_info(ctx.ppng, ctx.pinfo);
+	png_get_IHDR(ctx.ppng, ctx.pinfo, &width, &height, &bit_depth,
+	             &color_type, &ilace_type, &comp_type, &filter_method);
+
+	// check dimensions
+	if ((width * height) % 256 != 0) {
+		ConversionError("Invalid dimensions for palette: %dx%d = "
+		                "%d pixels; should be a multiple of 256",
+		                width, height, width * height);
+		goto fail;
+	}
+
+	num_palettes = width * height / 256;
+
+	// Convert all input files to RGB format.
+	png_set_strip_alpha(ctx.ppng);
+	if (color_type == PNG_COLOR_TYPE_PALETTE) {
+		png_set_palette_to_rgb(ctx.ppng);
+	}
+	if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) {
+		png_set_expand_gray_1_2_4_to_8(ctx.ppng);
+	}
+	if (bit_depth < 8) {
+		png_set_packing(ctx.ppng);
+	}
+
+	png_read_update_info(ctx.ppng, ctx.pinfo);
+
+	rowstep = png_get_rowbytes(ctx.ppng, ctx.pinfo);
+	rowbuf = checked_malloc(rowstep);
+	result = checked_calloc(1, sizeof(struct palette_set));
+	result->num_palettes = num_palettes;
+	result->palettes = checked_calloc(num_palettes, sizeof(struct palette));
+
+	for (y = 0; y < height; ++y) {
+		png_read_row(ctx.ppng, rowbuf, NULL);
+		for (x = 0; x < width; ++x) {
+			int pixel_num = y * width + x;
+			int pal_num = pixel_num / 256;
+			int color_num = pixel_num % 256;
+			struct palette_entry *ent =
+				&result->palettes[pal_num].entries[color_num];
+			ent->r = rowbuf[x * 3];
+			ent->g = rowbuf[x * 3 + 1];
+			ent->b = rowbuf[x * 3 + 2];
+		}
+	}
+
+	free(rowbuf);
+	png_read_end(ctx.ppng, NULL);
+
+fail:
+	V_ClosePNG(&ctx);
+	vfclose(input);
+	return result;
+}
+
+VFILE *PAL_ToImageFile(struct palette_set *set)
+{
+	VFILE *result = NULL;
+	struct png_context ctx;
+	uint8_t *rowbuf;
+	int w, h, x, y;
+
+	w = 256;
+	h = set->num_palettes;
+
+	result = V_OpenPNGWrite(&ctx);
+	if (result == NULL) {
+		goto fail;
+	}
+
+	png_set_IHDR(ctx.ppng, ctx.pinfo, w, h, 8, PNG_COLOR_TYPE_RGB,
+	             PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
+	             PNG_FILTER_TYPE_DEFAULT);
+	png_write_info(ctx.ppng, ctx.pinfo);
+
+	rowbuf = checked_calloc(w, 3);
+	for (y = 0; y < h; y++) {
+		for (x = 0; x < w; ++x) {
+			rowbuf[x * 3] = set->palettes[y].entries[x].r;
+			rowbuf[x * 3 + 1] = set->palettes[y].entries[x].g;
+			rowbuf[x * 3 + 2] = set->palettes[y].entries[x].b;
+		}
+		png_write_row(ctx.ppng, rowbuf);
+	}
+	free(rowbuf);
+
+	png_write_end(ctx.ppng, ctx.pinfo);
+	vfseek(result, 0, SEEK_SET);
+
+fail:
+	V_ClosePNG(&ctx);
+	return result;
+}

src/palette/palette.h

@@ -16,4 +16,13 @@ struct palette {
 	struct palette_entry entries[256];
 };
 
+// A collection of palettes - ie. the decoded contents of a PLAYPAL lump.
+struct palette_set {
+	struct palette *palettes;
+	size_t num_palettes;
+};
+
 extern const struct palette doom_palette;
+
+struct palette_set *PAL_FromImageFile(VFILE *input);
+VFILE *PAL_ToImageFile(struct palette_set *set);