{"id":16583,"date":"2022-10-20T11:03:46","date_gmt":"2022-10-20T05:33:46","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-merge-paint-results-in-thread-bitmap-painting\/"},"modified":"2022-10-20T11:03:46","modified_gmt":"2022-10-20T05:33:46","slug":"solved-merge-paint-results-in-thread-bitmap-painting","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-merge-paint-results-in-thread-bitmap-painting\/","title":{"rendered":"[Solved] merge paint results in thread bitmap painting"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-24389776\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"24389776\" data-parentid=\"24387662\" data-score=\"1\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<pre><code>    bitblt(Masterbitmap.Canvas.handle, 0, 0, XPixel, YPixel,\n      bitmap.Canvas.handle, 0, 0, srcand);\n<\/code><\/pre>\n<p>you explicitly called Masterbitmap.Canvas.Lock, however you didn&#8217;t call bitmap.Canvas.Lock (so you can loose the canvas handle anytime within this call&#8230;)<\/p>\n<p>Additionally, you need to consider thread safety within GDI itself: Sharing of any GDI objects between different threads should be avoided at all cost. For example if you select a bitmap into two different device contexts at the same time (but in different threads) you may run into problems within GDI itself&#8230;<\/p>\n<p>Please note that older versions of delphi don&#8217;t protect against sharing of cached handles (Font, Brush and Pen handles are cached within a global list. This was fixed in an XE3 service pack if I remember correctly).<\/p>\n<p>In short: I&#8217;d consider to avoid TCanvas and TBitmap completely if you really need multi-threading. (It&#8217;s much easier to be multi-threading safe that way)<\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">2<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved merge paint results in thread bitmap painting <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] bitblt(Masterbitmap.Canvas.handle, 0, 0, XPixel, YPixel, bitmap.Canvas.handle, 0, 0, srcand); you explicitly called Masterbitmap.Canvas.Lock, however you didn&#8217;t call bitmap.Canvas.Lock (so you can loose the canvas handle anytime within this call&#8230;) Additionally, you need to consider thread safety within GDI itself: Sharing of any GDI objects between different threads should be avoided at all cost. For &#8230; <a title=\"[Solved] merge paint results in thread bitmap painting\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-merge-paint-results-in-thread-bitmap-painting\/\" aria-label=\"More on [Solved] merge paint results in thread bitmap painting\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[3414,740,884],"class_list":["post-16583","post","type-post","status-publish","format-standard","hentry","category-solved","tag-bitmap","tag-delphi","tag-multithreading"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] merge paint results in thread bitmap painting - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-merge-paint-results-in-thread-bitmap-painting\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] merge paint results in thread bitmap painting - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] bitblt(Masterbitmap.Canvas.handle, 0, 0, XPixel, YPixel, bitmap.Canvas.handle, 0, 0, srcand); you explicitly called Masterbitmap.Canvas.Lock, however you didn&#8217;t call bitmap.Canvas.Lock (so you can loose the canvas handle anytime within this call&#8230;) Additionally, you need to consider thread safety within GDI itself: Sharing of any GDI objects between different threads should be avoided at all cost. 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For ... 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