57 lines
4.0 KiB
Plaintext
57 lines
4.0 KiB
Plaintext
[video output=day117 member=cmuratori stream_platform=twitch stream_username=handmade_hero project=code title="Packing Pixels for the Framebuffer" vod_platform=youtube id=90eSF6jLzvQ annotator=dspecht annotator=Miblo]
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[2:05][Load up the code and consider optimisation]
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[4:09][handmade_render_group.cpp: Comment out if(ShouldFill\[I\])]
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[5:34][Blackboard: Interleaving four SIMD values]
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[14:27][Blackboard: Establishing the order we need]
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[15:46][handmade_render_group.cpp: Write the SIMD register names that we want to end up with]
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[16:29][Internet: Intel Intrinsics Guide[ref
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site="Intel"
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page="Intrinsics Guide"
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url="https://software.intel.com/sites/landingpage/IntrinsicsGuide/"]]
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[17:23][Blackboard: __mm_unpackhi_epi32 and __mm_unpacklo_epi32]
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[19:04][Blackboard: Using these operations to generate what we need]
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[24:17][handmade_render_group.cpp: Name the registers in register order]
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[25:15][Internet: Double-check the parameter order of the unpack operations]
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[26:22][handmade_render_group.cpp: Start to populate the registers]
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[26:52][Internet: Keeping in mind how often you move between __m128 and __m128i]
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[28:39][handmade_render_group.cpp: Cast the Blended values from float to int]
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[29:47][Use structured art to enable us to see what's happening]
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[34:47][Debugger: Watch how our art gets shuffled]
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[38:40][handmade_render_group.cpp: Produce the rest of the pixel values we need]
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[41:43][Convert 32-bit floating point values to 8-bit integers]
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[44:07][// TODO(casey): Set the rounding to something known]
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[45:08][Blackboard: Using 8-bits of these 32-bit registers]
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[47:32][handmade_render_group.cpp: Bitwise OR and Shift these values]
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[50:27][Blackboard: How the shift operations work]
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[52:44][handmade_render_group.cpp: Implement these shifts]
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[55:06][Debugger: Take a look at the Out value]
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[57:33][handmade_render_group.cpp: Break out the values]
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[58:22][Debugger: Inspect these values]
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[58:35][handmade_render_group.cpp: Fix the test case]
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[59:32][Debugger: Inspect our stuff]
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[1:00:13][handmade_render_group.cpp: Write Out to Pixel]
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[1:01:08][Debugger: Crash and reload]
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[1:01:43][Debugger: Note that we are writing unaligned]
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[1:04:22][Blackboard: Alignment]
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[1:05:54][handmade_render_group.cpp: Issue _mm_storeu_si128 to cause the compiler to use the (unaligned) mov instruction]
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[1:07:23][Recap and glimpse into the future]
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[1:08:30][Q&A][:speech]
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[1:09:59][@braincruser][Will the operations be reordered to reduce the number of ops and load / stores?]
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[1:12:01][@mmozeiko][You are calculating Out like or(or(or(r, g), b), a). Would it be better to do it like this: or(or(r, g), or(b, a)), so first two or's are not dependent on each other?]
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[1:14:57][handmade_render_group.cpp: Write it the way mmozeiko suggests]
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[1:17:31][@uspred][Do you need to start with 32-bit floats? Is there further optimization that doesn't need the casting?]
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[1:18:21][Blackboard: Multiplying floats vs Multiplying integers]
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[1:19:54][@mmozeiko][Same for texture bilinear adds together]
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[1:20:03][handmade_render_group.cpp: Implement mmozeiko's suggestion]
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[1:23:00][@flaturated][Can you compile /O2 to compare it to last week's performance?]
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[1:23:16][@brblackmer][Why did you make macros for your SIMD operations (mmSquare, etc.) vs making functions?]
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[1:23:39][@quikligames][Are these intrinsics the same on other operating systems or compilers, as long as it's using Intel architecture?]
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[1:24:40][@mmozeiko][Why do you say unaligned store is nasty? As far as I know, for latest Intel CPUs (at least starting from Ivy Bridge) unaligned load / store is not very expensive anymore (<5% difference)]
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[1:26:25][@plain_flavored][Is scalar access to __m128 elements still slow on Intel?]
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[1:27:18][@braincruser][The processor window is 192 instructions]
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[1:28:01][@gasto5][I don't understand how one optimizes by using the intrinsic or function]
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[1:28:51][@mmozeiko][_mm_cvttps_epi32 always truncates. Would that be better than messing with rounding mode?]
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[1:30:45][handmade_render_group.cpp: Switch to _mm_cvttps_epi32]
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[1:32:50][Wrap up][:speech]
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[/video]
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