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In 1984 Sierra introduced the original "King's Quest: Quest for the Crown" to showcase the expanded abilities of IBM's new computer, the '''PCjr'''<ref>[[w:PCjr|PCjr article on Wikipedia]]</ref>. In fact, the first couple of releases were published by IBM. The '''A'''dventure '''G'''ame '''I'''nterpreter (AGI) was developed as the new engine for this task. AGI's graphics were 160px x 200px by 16 colors (quadrupedal that of CGA's 4 colors) using '''vector graphics'''<ref>[[w:Vector graphics|Vector Graphics article on Wikipedia]]</ref> backgrounds. It also had three voice with noise channel sound. This was quite a technological advancement and even cutting edge at the time. AGI was designed for portability (easy to port to other platforms.) It became Sierra's main game engine until the advent of Sierra's next engine, SCI. Most of Sierra's famous series began in the AGI era.
In 1984 Sierra introduced the original "King's Quest: Quest for the Crown" to showcase the expanded abilities of IBM's new computer, the '''PCjr'''<ref>[[w:PCjr|PCjr article on Wikipedia]]</ref>. In fact, the first couple of releases were published by IBM. The '''A'''dventure '''G'''ame '''I'''nterpreter (AGI) was developed as the new engine for this task. AGI's graphics were 160px x 200px by 16 colors (quadrupedal that of CGA's 4 colors) using '''vector graphics'''<ref>[[w:Vector graphics|Vector Graphics article on Wikipedia]]</ref> backgrounds. It also had three voice with noise channel sound. This was quite a technological advancement and even cutting edge at the time. AGI was designed for portability (easy to port to other platforms.) It became Sierra's main game engine until the advent of Sierra's next engine, SCI. Most of Sierra's famous series began in the AGI era.
<!-- <div align="center">[https://www.youtube.com/watch?v=qdbdGJBwpgs King's Quest : Quest for the Crown Intro (AGI)]</div> -->
Hardware began to advance beyond what AGI could utilize, so Sierra began development on its next engine, '''SC'''ript '''I'''nterpreter or later [[Sierra Creative Interpreter|'''S'''ierra '''C'''reative '''I'''nterpreter (SCI)]]. The previous year before the last official AGI game, "[[Manhunter 2: San Francisco]]" in 1989, Sierra released the first SCI (SCI0) game, "[[King's Quest IV: The Perils of Rosella]]" in 1988. In keeping with '''Moore's Law'''<ref>[[w:Moore%27s_Law|Moore's Law on Wikipedia]]</ref>, SCI could take advantage of the constantly increasing capabilities of the new hardware. As with AGI in its day, SCI was a big leap forward in technology. The higher resolution allowed for better graphics. Even though 200px x 320px may not seem that much over AGI's 160px x 200px, it is very noticeable.
Hardware began to advance beyond what AGI could utilize, so Sierra began development on its next engine, '''SC'''ript '''I'''nterpreter or later [[Sierra Creative Interpreter|'''S'''ierra '''C'''reative '''I'''nterpreter (SCI)]]. The previous year before the last official AGI game, "[[Manhunter 2: San Francisco]]" in 1989, Sierra released the first SCI (SCI0) game, "[[King's Quest IV: The Perils of Rosella]]" in 1988. In keeping with '''Moore's Law'''<ref>[[w:Moore%27s_Law|Moore's Law on Wikipedia]]</ref>, SCI could take advantage of the constantly increasing capabilities of the new hardware. As with AGI in its day, SCI was a big leap forward in technology. The higher resolution allowed for better graphics. Even though 200px x 320px may not seem that much over AGI's 160px x 200px, it is very noticeable.
Sierra co-developed King's Quest IV in both AGI and SCI. If the hardware requirements were too high for a user's PC, he could send in his SCI game for the AGI version. Here are side by side comparisons of the two versions:
Sierra co-developed King's Quest IV in both AGI and SCI. If the hardware requirements were too high for a user's PC, he could send in his SCI game for the AGI version. Here are side by side comparisons of the two versions:
KQ4 SCI version 1.006.004 was able to use additional partial PIC resources overlayed on top of the normal daytime PIC resource, such as a dark sky with stars to add a darker sky with stars and covering other lighter colors with darker ones, etc. to create a composite for the night PIC. SCI0 generally did not use a complete second resource the way AGI did. Note that the teal color in the overlay PICTURE resource is set to be transparent. Anything in the base Pic under the teal would show.
KQ4 SCI version 1.006.004 was able to use additional partial PIC resources overlayed on top of the normal daytime PIC resource, such as a dark sky with stars to add a darker sky with stars and covering other lighter colors with darker ones, etc. to create a composite for the night PIC. SCI0 generally did not use a complete second resource the way AGI did. Note that the teal color in the overlay PICTURE resource is set to be transparent. Anything in the base Pic under the teal would show.
During the transition to VGA, Sierra released both EGA and VGA versions of the same games. Some of these had artwork that were completely done for both versions. The end result was better optimized for the EGA users, as in ''[[Jones in the Fast Lane]]''.
During the transition to VGA, Sierra released both EGA and VGA versions of the same games. Some of these had artwork that were completely done for both versions. The end result was better optimized for the EGA users, as in ''[[Jones in the Fast Lane]]''.
Besides more detailed images and VGA's 256 color palette allowing more accurate colors, the expanded color depth allowed palette switching to simulate even more colors and being able to modify an existing picture resource by changing the palette it used. They could simulate a day/night cycle by merely changing the palette, while using the same PICTURE resource. The same method was used to add dawn and dusk scenes, as well.
Besides more detailed images and VGA's 256 color palette allowing more accurate colors, the expanded color depth allowed palette switching to simulate even more colors and being able to modify an existing picture resource by changing the palette it used. They could simulate a day/night cycle by merely changing the palette, while using the same PICTURE resource. The same method was used to add dawn and dusk scenes, as well.
| align="center" |''Half Dome Logo from [[Quest for Glory 1 VGA]]''
| align="center" |''Half Dome Logo from [[Quest for Glory 1 VGA|320px]]''
| align="center" |''<nowiki>'Enry the 'Ermite's</nowiki> Cave''
| align="center" |''<nowiki>'Enry the 'Ermite's</nowiki> Cave''
|}
|}
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With SCI2, around the time of "Gabriel Knight: Sins of the Fathers", [[w:VESA|VESA]] support was added, giving SCI a 640px x 480px resolution. The first VESA games used a mixture of VGA and VESA graphics. Using the VESA driver or a Windows interpreter, the 320px x 200px graphics were scaled up, overlaying higher resolution graphics for things like GUI items on top. The VGA to VESA transitional games would have two sets of resources, one lower res for VGA and a higher one for VESA.
With SCI2, around the time of "Gabriel Knight: Sins of the Fathers", [[w:VESA|VESA]] support was added, giving SCI a 640px x 480px resolution. The first VESA games used a mixture of VGA and VESA graphics. Using the VESA driver or a Windows interpreter, the 320px x 200px graphics were scaled up, overlaying higher resolution graphics for things like GUI items on top. The VGA to VESA transitional games would have two sets of resources, one lower res for VGA and a higher one for VESA.
Later versions of SCI32 used Windows SVGA<ref>[[w:SVGA|SVGA on wikipedia]]</ref> and/or DOS VESA<ref>[[w:VESA|VESA on Wikipedia]]</ref> at 640px x 480px only.
Later versions of SCI32 used Windows SVGA<ref>[[w:SVGA|SVGA on wikipedia]]</ref> and/or DOS VESA<ref>[[w:VESA|VESA on Wikipedia]]</ref> at 640px x 480px only.
''Note that while the pixel dimensions mentioned are not proportional, the aspect ratio<ref>[[w:Aspect ratio|Aspect ratio on Wikipedia]]</ref> for these games is 4:3. The monitors from the different eras had differently shaped pixels, but the same overall dimensions''
''Note that while the pixel dimensions mentioned are not proportional, the aspect ratio<ref>[[w:Aspect ratio|Aspect ratio on Wikipedia]]</ref> for these games is 4:3. The monitors from the different eras had differently shaped pixels, but the same overall ratio''
Note: for simplicity, this article is limited to ports of AGI's and SCI's main target platform, the PC.
Many of the Sierra On-Line games before AGI used the then standard 4 color CGA[1] graphics and single voice sound via the PC speaker.
AGI
In 1984 Sierra introduced the original "King's Quest: Quest for the Crown" to showcase the expanded abilities of IBM's new computer, the PCjr[2]. In fact, the first couple of releases were published by IBM. The Adventure Game Interpreter (AGI) was developed as the new engine for this task. AGI's graphics were 160px x 200px by 16 colors (quadrupedal that of CGA's 4 colors) using vector graphics[3] backgrounds. It also had three voice with noise channel sound. This was quite a technological advancement and even cutting edge at the time. AGI was designed for portability (easy to port to other platforms.) It became Sierra's main game engine until the advent of Sierra's next engine, SCI. Most of Sierra's famous series began in the AGI era.
The KQ4AGI day/night cycle had to be done with two distinct PICTURE (background) resources, one for day and one for night.
SCI
Hardware began to advance beyond what AGI could utilize, so Sierra began development on its next engine, SCript Interpreter or later Sierra Creative Interpreter (SCI). The previous year before the last official AGI game, "Manhunter 2: San Francisco" in 1989, Sierra released the first SCI (SCI0) game, "King's Quest IV: The Perils of Rosella" in 1988. In keeping with Moore's Law[4], SCI could take advantage of the constantly increasing capabilities of the new hardware. As with AGI in its day, SCI was a big leap forward in technology. The higher resolution allowed for better graphics. Even though 200px x 320px may not seem that much over AGI's 160px x 200px, it is very noticeable.
Technologically, another huge advance was SCI's object oriented scripting language[5] (AGI was a procedural language[6]), which allowed for much more complex scripting, opening possibilities the developers could have only dreamt of earlier.
Sierra co-developed King's Quest IV in both AGI and SCI. If the hardware requirements were too high for a user's PC, he could send in his SCI game for the AGI version. Here are side by side comparisons of the two versions:
King's Quest IV: The Perils of Rosella SCI Intro (YouTube)
SCI0
SCI0 is the first version of the interpreter used. While still just 16 colors (EGA[7]), but SCI0 introduced dithering, which mixed pixels of different colors into the same fill areas that gave the effect of more than 16 colors. Most importantly, support for the new sound cards. With SCI, music became an inseparable part of Sierra games. Even though the first exposure most had was with AdLib's hoots and honks, it also supported the MPU-401, which allowed Sierra's composers to create some amazing Roland MT-32 sound tracks.
SCI0 Day/Night Cycles
Like AGI, KQ4 SCI early versions (1.000.111) used two distinct PICTURE resources, too.
KQ4 SCI version 1.006.004 was able to use additional partial PIC resources overlayed on top of the normal daytime PIC resource, such as a dark sky with stars to add a darker sky with stars and covering other lighter colors with darker ones, etc. to create a composite for the night PIC. SCI0 generally did not use a complete second resource the way AGI did. Note that the teal color in the overlay PICTURE resource is set to be transparent. Anything in the base Pic under the teal would show.
SCI Advances
Sierra was able to continually expand SCI's capabilities as hardware advanced. Slightly before the transition from SCI0 to SCI1, digital sound was added, and the characters began to speak.
During the transition to VGA, Sierra released both EGA and VGA versions of the same games. Some of these had artwork that were completely done for both versions. The end result was better optimized for the EGA users, as in Jones in the Fast Lane.
Later VGA games simply took the VGA graphics and reduced the palette.
SCI1-SCI1.1 Day/Night Cycles
Besides more detailed images and VGA's 256 color palette allowing more accurate colors, the expanded color depth allowed palette switching to simulate even more colors and being able to modify an existing picture resource by changing the palette it used. They could simulate a day/night cycle by merely changing the palette, while using the same PICTURE resource. The same method was used to add dawn and dusk scenes, as well.
SCI1.1 Palette Cycling
SCI1.1's 256 color palette allows palette cycling[10]. By cycling colors used in the palette animation effects could be achieved. This is probably best known in the Half Dome logo intro used in SCI1.1 and later games. It was often used to animate backgrounds as well, as in the scene from inside 'Enry the 'Ermite's cave from QfG1VGA
For more information see the SCI Companion entry on Palette Cycling
SCI1 Digital Audio
SCI1 also introduced full speech, initially via Redbook CD Audio tracks as with Jones in the Fast Lane. Later games used audio resources on the same data track as the game, starting with King's Quest V
SCI2
With SCI2, around the time of "Gabriel Knight: Sins of the Fathers", VESA support was added, giving SCI a 640px x 480px resolution. The first VESA games used a mixture of VGA and VESA graphics. Using the VESA driver or a Windows interpreter, the 320px x 200px graphics were scaled up, overlaying higher resolution graphics for things like GUI items on top. The VGA to VESA transitional games would have two sets of resources, one lower res for VGA and a higher one for VESA.
SCI32
Later versions of SCI32 used Windows SVGA[11] and/or DOS VESA[12] at 640px x 480px only.
Note that while the pixel dimensions mentioned are not proportional, the aspect ratio[13] for these games is 4:3. The monitors from the different eras had differently shaped pixels, but the same overall ratio
Leisure Suit Larry 7: Love for Sail Opening Credits (YouTube)
Often the interpreter was modified, improved or features added to meet the needs of a game in development. This could cause the engine to become so specific to that game that the the source code for the engine would be stored with the source for the game.
