Difference between revisions of "AGI/Specifications/Other/AGI256/Implementation Details"

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AGI/Specifications/Other/AGI256/Implementation Details (view source)

Revision as of 08:46, 18 July 2007

2,959 bytes added , 08:46, 18 July 2007

Fixed a typo. Hadn't put & in front of some code where it should have been.

Buddha^

417

edits

@@ Line 1: / Line 1: @@
 In the original PC AGI interpreter v2.936 the engine holds the color and priority/control
-line information for each pixel in a 160x200 byte buffer. The color data for each pixel
+line information for each pixel in a 160x168 byte buffer. The color data for each pixel
 is held in the byte's lower 4 bits and the priority/control line data is held in the upper
 bits.
-AGI256 extends this 160x200 byte buffer to a 320x200 byte buffer so that the 256-color
+AGI256 extends this 160x168 byte buffer to a 320x168 byte buffer so that the 256-color
-data is held in the right 160x200 half of the buffer and the original style 16-color and
+data is held in the right 160x168 half of the buffer and the original style 16-color and
-priority/control line information is held in the left 160x200 half of the buffer.
+priority/control line information is held in the left 160x168 half of the buffer.
+When loading 256-color picture resource with the unknown170 command
+the picture is loaded straight into the right 160x168 half of the 320x168 memory buffer.
+Cel blitting routine is modified so that when sprite data would normally be written
+to a position (x, y) in the 16-color buffer (i.e. the left 160x168 half) it's actually
+written to the same position (x, y) but in the 256-color buffer (i.e. the right 160x168 half).
 ==Used external info==
@@ Line 25: / Line 32: @@
 * AGIDATA.OVL
+===Reverse engineered C version of AGI256's AGIOBJS.OVL===
+Things may be wrong, misleading etc. Caveat emptor.
+This is the cel blitting routine from AGIOBJS.OVL.
+<pre>
+struct blitStruct {
+	uint8 b0;
+	uint8 b1;
+	uint8 notEgo; // Sort of a guess based on variable's usage, may also be dontUpdateEgoVisibility or something like that
+	uint16 xPos;
+	uint16 yPos; // Is this named correctly?
+	uint8 b7;
+	uint8 b8;
+	uint8 b9;
+	uint8 b10;
+	uint8 b11;
+	uint8 b12;
+	uint8 b13;
+	uint8 b14;
+	uint8 b15;
+	struct celStruct *celPtr; // Offset into segment DS really, 16 bits
+	uint8 b18;
+	uint8 b19;
+	uint8 b20;
+	uint8 b21;
+	uint8 b22;
+	uint8 b23;
+	uint8 b24;
+	uint8 b25;
+	uint8 b26;
+	uint8 b27;
+	uint8 b28;
+	uint8 b29;
+	uint8 b30;
+	uint8 b31;
+	uint8 b32;
+	uint8 b33;
+	uint8 b34;
+	uint8 b35;
+	uint8 celPriority;
+};
+struct celStruct {
+	uint8 width; // This is a guess
+	uint8 height;
+	union {
+		uint8 flags; // Uses values from enum flagsEnum
+		uint8 transparentColor; // Only lower 4 bits
+	};
+	uint8 rleData[?];
+};
+enum flagsEnum {
+	F_MIRROR = 1 << 7;
+};
+#define _WIDTH 160
+#define _HEIGHT 168
+uint16 screenOffset(uint8 x, uint8 y) {
+	return y * (_WIDTH * 2) + x;
+}
+void agi256BlitCel(struct blitStruct *s) {
+	uint8 *pic = &agi256PicSeg[0];
+	const uint16 endPos = (_WIDTH * 2) * (_HEIGHT - 1); // I would have put (((_WIDTH * 2) * (_HEIGHT - 1)) - _WIDTH) here
+	bool celInvisible = true;
+	uint8 height = s->celPtr->height;
+	uint8 celPriority = s->celPriority;
+	if (s->celPtr->flags & F_MIRROR) // Test for mirroring
+		blitMirrorCell();
+	uint8 *rleData = s->celPtr->rleData;
+	uint16 pos = screenOffset(s->xPos, s->yPos - height + 1);
+	uint8 transparentColor = s->celPtr->transparentColor;
+	do {
+		uint16 oldPos = pos;
+		while (uint8 rleByte = *(rleData++)) { // rleByte != 0
+			uint8 runColor = rleByte >> 4;
+			uint8 runLength = rleByte & 0x0f;
+			if (runColor == transparentColor) { // Check for transparency
+				pos += runLength;
+			} else do {
+				uint8 pixelPriority = pic[pos] >> 4; // Read pixel's priority/control line info
+				if (pixelPriority < 3) {
+					pixelPriority = 0;
+					for (uint16 ySearchPos = pos + _WIDTH * 2;
+						ySearchPos < endPos && (pixelPriority = pic[ySearchPos] >> 4) < 3;
+						ySearchPos += _WIDTH * 2);
+				}
+				if (celPriority >= pixelPriority) {
+					pic[pos + _WIDTH] = runColor;
+					celInvisible = false;
+				}
+				pos++;
+			} while (--runLength > 0);
+		}
+		pos = oldPos + _WIDTH * 2;
+	} while (--height > 0);
+	if (!s->notEgo)
+		setFlag(f1, celInvisible);
+}
+</pre>
 ===Differences between AGI v2.936's AGIDATA.OVL and AGI256's AGIDATA.OVL===
@@ Line 799: / Line 920: @@
 codeseg:9DB0                 jmp     AO_agi256_saveArea ; savearea(struct Sprite *s) {
 codeseg:9DB0 j_AO_agi256_saveArea endp               ;   int srcOffset = screenOffset(s->xPos, s->yPos);
-codeseg:9DB0                                         ;   uint8 *src = agi256PicSeg[srcOffset + 160];
+codeseg:9DB0                                         ;   uint8 *src = &agi256PicSeg[srcOffset + 160];
 codeseg:9DB0                                         ;   for (int y = 0; y < s->ySize; y++)
 codeseg:9DB0                                         ;     memcpy(s->buffer + s->xSize * y, src + 320 * y, s->xSize);
@@ Line 831: / Line 952: @@
 codeseg:9DB9 ; savearea(struct Sprite *s) {
 codeseg:9DB9 ;   int srcOffset = screenOffset(s->xPos, s->yPos);
-codeseg:9DB9 ;   uint8 *src = agi256PicSeg[srcOffset + 160];
+codeseg:9DB9 ;   uint8 *src = &agi256PicSeg[srcOffset + 160];
 codeseg:9DB9 ;   for (int y = 0; y < s->ySize; y++)
 codeseg:9DB9 ;     memcpy(s->buffer + s->xSize * y, src + 320 * y, s->xSize);

Difference between revisions of "AGI/Specifications/Other/AGI256/Implementation Details"

AGI/Specifications/Other/AGI256/Implementation Details (view source)

Revision as of 08:46, 18 July 2007

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