[{"id":36453,"web_url":"https://patchwork.libcamera.org/comment/36453/","msgid":"<857bwk81ov.fsf@mzamazal-thinkpadp1gen7.tpbc.csb>","date":"2025-10-24T20:49:52","subject":"Re: [PATCH v3 31/39] libcamera: shaders: Fix neighbouring positions\n\tin 8-bit debayering","submitter":{"id":177,"url":"https://patchwork.libcamera.org/api/people/177/","name":"Milan Zamazal","email":"mzamazal@redhat.com"},"content":"Bryan O'Donoghue writes:\n\n> From: Milan Zamazal \n>\n> When accessing a texture position in a shader, the pixel with the\n> nearest centre to the specified texture coordinates (as mandated by\n> specifying GL_NEAREST parameter) is taken. The current vertex shader\n> determines the positions of the neighbouring pixels by adding the\n> provided texture steps to the exact centre pixel coordinates. But this\n> places the computed coordinates, from the point of view of GL_NEAREST,\n> exactly between the pixels and is thus prone to floating point\n> inaccuracies. Wrong neighbouring pixel coordinates may be used,\n> resulting in artefacts in the output image.\n\nI cannot reproduce this any more. Quite opposite, artefacts are not\npresent iff the corrective step multiplication step is inside -0.5..0.5\nrange. So the coordinates are apparently placed on pixel centres rather\nthan borders now. And if I attempt to use a second set of shaders, the\ncoordinates shift introduced by this patch causes another trouble with\nartefacts (still no idea why).\n\nHonestly, I don't understand how it is supposed to work and what has\nchanged that it works differently now than long time before (pre-v1, I\nthink). But based on my recent empiric observations, I'd say we should\ndrop this patch (unless independent testing tells otherwise).\n\n> Let's fix the problem by shifting the initial coordinates a bit from the\n> pixel border.\n>\n> Signed-off-by: Milan Zamazal \n> Signed-off-by: Bryan O'Donoghue \n> ---\n> include/libcamera/internal/shaders/bayer_unpacked.vert | 8 ++++----\n> 1 file changed, 4 insertions(+), 4 deletions(-)\n>\n> diff --git a/include/libcamera/internal/shaders/bayer_unpacked.vert b/include/libcamera/internal/shaders/bayer_unpacked.vert\n> index fb5109ee..fc1cf89f 100644\n> --- a/include/libcamera/internal/shaders/bayer_unpacked.vert\n> +++ b/include/libcamera/internal/shaders/bayer_unpacked.vert\n> @@ -44,10 +44,10 @@ void main(void) {\n> center.xy = textureIn;\n> center.zw = textureIn * tex_size + tex_bayer_first_red;\n> \n> - xCoord = center.x + vec4(-2.0 * tex_step.x,\n> - -tex_step.x, tex_step.x, 2.0 * tex_step.x);\n> - yCoord = center.y + vec4(-2.0 * tex_step.y,\n> - -tex_step.y, tex_step.y, 2.0 * tex_step.y);\n> + xCoord = center.x + 0.1 * tex_step.x +\n> + vec4(-2.0 * tex_step.x, -tex_step.x, tex_step.x, 2.0 * tex_step.x);\n> + yCoord = center.y + 0.1 * tex_step.y +\n> + vec4(-2.0 * tex_step.y, -tex_step.y, tex_step.y, 2.0 * tex_step.y);\n> \n> gl_Position = proj_matrix * vertexIn;\n> }","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 45436BE080\n\tfor ;\n\tFri, 24 Oct 2025 20:50:03 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 82461609E7;\n\tFri, 24 Oct 2025 22:50:02 +0200 (CEST)","from us-smtp-delivery-124.mimecast.com\n\t(us-smtp-delivery-124.mimecast.com [170.10.129.124])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 1C67660990\n\tfor ;\n\tFri, 24 Oct 2025 22:50:00 +0200 (CEST)","from mail-ej1-f70.google.com (mail-ej1-f70.google.com\n\t[209.85.218.70]) by relay.mimecast.com with ESMTP with STARTTLS\n\t(version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id\n\tus-mta-467-77SI4DS7ODKwjMmbjaDvFA-1; Fri, 24 Oct 2025 16:49:57 -0400","by mail-ej1-f70.google.com with SMTP id\n\ta640c23a62f3a-b6d52387ebeso287951666b.1\n\tfor ;\n\tFri, 24 Oct 2025 13:49:57 -0700 (PDT)","from mzamazal-thinkpadp1gen7.tpbc.csb\n\t(ip-77-48-47-2.net.vodafone.cz. 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The current vertex shader\n>> determines the positions of the neighbouring pixels by adding the\n>> provided texture steps to the exact centre pixel coordinates. But this\n>> places the computed coordinates, from the point of view of GL_NEAREST,\n>> exactly between the pixels and is thus prone to floating point\n>> inaccuracies. Wrong neighbouring pixel coordinates may be used,\n>> resulting in artefacts in the output image.\n> I cannot reproduce this any more. Quite opposite, artefacts are not\n> present iff the corrective step multiplication step is inside -0.5..0.5\n> range. So the coordinates are apparently placed on pixel centres rather\n> than borders now. And if I attempt to use a second set of shaders, the\n> coordinates shift introduced by this patch causes another trouble with\n> artefacts (still no idea why).\n> \n> Honestly, I don't understand how it is supposed to work and what has\n> changed that it works differently now than long time before (pre-v1, I\n> think). But based on my recent empiric observations, I'd say we should\n> drop this patch (unless independent testing tells otherwise).\n\nOK.\n\nI trust your debug here and rely on your input for this setup anyway.\n\nDropped.\n\n---\nbod","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 22C8BC3259\n\tfor ;\n\tSat, 25 Oct 2025 00:27:27 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 6682E609E0;\n\tSat, 25 Oct 2025 02:27:26 +0200 (CEST)","from mail-ed1-x531.google.com (mail-ed1-x531.google.com\n\t[IPv6:2a00:1450:4864:20::531])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 429AC607ED\n\tfor ;\n\tSat, 25 Oct 2025 02:27:25 +0200 (CEST)","by mail-ed1-x531.google.com with SMTP id\n\t4fb4d7f45d1cf-63c12ff0c5eso5341059a12.0\n\tfor ;\n\tFri, 24 Oct 2025 17:27:25 -0700 (PDT)","from [192.168.0.163] (188-141-3-146.dynamic.upc.ie.\n\t[188.141.3.146]) by smtp.gmail.com with ESMTPSA id\n\t4fb4d7f45d1cf-63e7efb9fa6sm426428a12.31.2025.10.24.17.27.23\n\t(version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128);\n\tFri, 24 Oct 2025 17:27:23 -0700 (PDT)"],"Authentication-Results":"lancelot.ideasonboard.com; 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\n\tFri, 24 Oct 2025 17:27:24 -0700 (PDT)","Message-ID":"<461cb3b0-1cb0-4ef8-b396-d8b8954167ab@linaro.org>","Date":"Sat, 25 Oct 2025 01:27:22 +0100","MIME-Version":"1.0","User-Agent":"Mozilla Thunderbird","Subject":"Re: [PATCH v3 31/39] libcamera: shaders: Fix neighbouring positions\n\tin 8-bit debayering","To":"Milan Zamazal ","Cc":"libcamera-devel@lists.libcamera.org, hdegoede@redhat.com,\n\tbod.linux@nxsw.ie","References":"<20251015012251.17508-1-bryan.odonoghue@linaro.org>\n\t<20251015012251.17508-32-bryan.odonoghue@linaro.org>\n\t<857bwk81ov.fsf@mzamazal-thinkpadp1gen7.tpbc.csb>","From":"Bryan O'Donoghue ","Content-Language":"en-US","In-Reply-To":"<857bwk81ov.fsf@mzamazal-thinkpadp1gen7.tpbc.csb>","Content-Type":"text/plain; charset=UTF-8; format=flowed","Content-Transfer-Encoding":"7bit","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}}]