Raster Manipulation via Horizontal Blank Direct Memory Access
Source video: It Took Every SNES Hardware Trick To Make My Game (Inkbox, 51:14) · at 35:11. The video explains HDMA for the title screen clouds on layer 2, not for layer 3 in the game.
Parent section: Video Structure and Narrative Progression
To simulate three-dimensional environmental depth on flat tilemaps, the presentation explores Direct Memory Access (DMA) and Horizontal Blank DMA (HDMA)1. Standard DMA transfers are restricted to the vertical blanking interval (V-Blank), whereas HDMA operates during the brief horizontal blanking periods between individual CRT scanline draws1. Inkbox demonstrates how HDMA channels are configured to update horizontal scroll registers scanline by scanline1. By mapping 16×16 graphic tiles across a 32×32 virtual playfield and modulating the horizontal displacement of Background Layer 3 down the display, the engine produces smooth, multi-plane mountain parallax effects without consuming central processor cycles during active rasterization1.
Review findings for this part
Section titled “Review findings for this part”The findings come from ../../findings/ (pass 1). The script matches them to this part by source line.
| ID | Severity | Evidence | Status | Location | Problem |
|---|---|---|---|---|---|
| D14-C1 | critical | VIDEO KNOW DOC | open | L27, L58, L84, L111, L117-133, L179 | Claim: HDMA writes register $2111 (BG3HOFS) for mountain parallax in the game, with bands at scanlines 60, 120, 160 and 210 and rates dx0.25 and dx0.50. Problem: The video puts the parallax on the title screen, not in the game (34:08). The far mountains sit on layer 3, and the clouds that scroll sit on layer 2 (34:28). At 35:31 Inkbox says that he writes “the background two horizontal scroll register”. That register is $210F, not $2111. The table has three bytes per entry: a line count and a two-byte value (35:51). The scanline numbers and the rates in the diagram are not in the video. In the game, the only HDMA scroll effect moves the inventory selection on layer 2 (33:47, 36:31). |
| D14-C6 | critical | DOC VERIFY | verify | L5-203 (all citations) | Claim: Each sentence cites “1”, and the text names the video as the subject. Problem: Source 1 is the techeblog news article, not the video. The video is source 3, and the text cites it only three times together with 1 (L62, L63, L184). The reviewer fetched source 1. It is a short summary that mentions HDMA, mode 1, 128 sprites and five plus three voices. It says nothing about spatial hashing, color math, priority cycling, emulator divergence or compilers. So most citations point to a source that does not hold the claim. A “video breakdown” that cites a news article for the video is not a breakdown of the video. |
| D14-M7 | major | VIDEO | open | L11-47, L203 | Claim: The video “follows nine distinct technical stages”, begins with the CPU architecture and the lack of an OS, and ends with the ROM release and the driver repository. Problem: The video begins with a recap and game design: fewer buttons, the attack blind spot, animation timing (00:26 to 02:48). The audio part is in the middle (08:40 to 19:30), not at the end. The video ends with the cartridge parts, the music of Dr. Matt, the free release, a poll about a physical release, and the PC Engine (45:03 to 50:53). The nine stages are the structure of the document, not of the video. |
| D14-M8 | major | VIDEO | open | L23, L27, L84, L104, L111, L178 | Claim: In the game, layer 3 holds “distant mountain art” with HDMA parallax. The 16 x 16 tiles on a 32 x 32 tilemap belong to the HDMA setup. Problem: In the game, layer 1 holds the environment and layer 2 the HUD (04:10). Layer 3 holds black tiles for the darkening trick (37:13). The mountains on layer 3 exist only on the title screen (34:28). The 16 x 16 tiles and the 32 x 32 tilemap belong to the scroll engine (04:30), where a 128 x 112 pixel box around the player drives the tile streaming (04:50). |
Review worksheet
Section titled “Review worksheet”1. Goal of this part
Section titled “1. Goal of this part”What does this part try to show, or help the reader decide?
2. Key claims to test
Section titled “2. Key claims to test”| # | Claim | Evidence given (citation / data) | Verifiable? |
|---|---|---|---|
| 1 |
3. Adversarial review
Section titled “3. Adversarial review”- Strongest counter-argument:
- Unsupported, overstated, or outdated claims:
- Source quality (primary vs. blog/forum/marketing):
- Omissions / what a skeptic would ask:
- Internal consistency with other segments:
4. Evaluation
Section titled “4. Evaluation”- Does the segment achieve its goal? (Yes / Partly / No)
- Confidence: (High / Medium / Low)
- Required fixes: