AshleyScirra
commented
2 years ago This is currently by design. Image recompression happens for entire spritesheets. If the spritesheet has over 256 colors, it won't be able to recompress to PNG-8. (This is still effective if the entire game, or at least most of the game, uses a fixed 256 color palette). There isn't any promise or guarantee you'll definitely get this; it's an optimisation that just works whenever it can.
Construct could in theory split the spritesheet up, but then you lose the optimisation benefits of spritesheets. Splitting up spritesheets can also actually cause the file size to become larger: repeated content in the same spritesheet can be compressed away, but repeated content across individual images must be re-encoded repeatedly. I think the current approach is the best trade-off between inefficient spritesheets and a possibly (but not guaranteed) smaller file-size, or efficient spritesheets and a possibly (but not guaranteed) larger file size, particularly since it's still effective if the entire game uses a fixed 256 color palette, and splitting vs. merging spritesheets does not always have a clear effect on file size.
Problem description
PNG-8 compression doesn't occur.
Attach a .c3p
recompression_image_bug_r268s.zip
Steps to reproduce
Observed result
Construct merged two images in one spritesheet which size is 8,02 KB.
Expected result
There should be two images: one is 156 byte, the other is 5,74 KB totaling less than 8,02 KB.
More details
According to this article: https://www.construct.net/en/tutorials/construct-3s-export-4
Next, all PNG images are run through a tool called OptiPNG, which tries lots of different ways to compress the image and picks whichever results in the smallest file size. This often gets an automatic and lossless 10-15% saving on the download size, but can take a long time. It's also able to losslessly palette-reduce 32-bit PNGs to 8-bit PNGs when the image has 256 colors or fewer, resulting in a much smaller file size, which is particularly effective for art styles which don't use many colors, like retro style pixel art. If you turn off the image recompression option on export, this step is skipped. This can make exports very quick, but can also make the download size significantly larger.
Is there a chance that the way Construct did this uses less memory in a game?
Affected browsers/platforms: Chrome
First affected release: broke in r268s
System details
View details
Platform information Browser: Chrome Browser version: 95.0.4638.54 Browser engine: Chromium Context: browser Operating system: Windows Operating system version: 7 Device type: desktop Device pixel ratio: 1 Logical CPU cores: 2 Approx. device memory: 4 GB User agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.54 Safari/537.36 C3 release: r268 (stable) Language setting: en-US Local storage Storage quota (approx): 59 gb Storage usage (approx): 602 mb (1%) Persistant storage: No Browser support notes This list contains missing features that are not required, but could improve performance or user experience if supported. UI effects are disabled in settings. WebGL 2+ is not supported. Rendering quality and features may be affected. WebGL information Version string: WebGL 1.0 (OpenGL ES 2.0 Chromium) Numeric version: 1 Supports NPOT textures: partial Supports GPU profiling: no Supports highp precision: yes Vendor: Google Inc. (Intel) Renderer: ANGLE (Intel, Intel(R) HD Graphics Direct3D9Ex vs_3_0 ps_3_0, igdumdim64.dll-10.18.10.4653) Major performance caveat: no Maximum texture size: 8192 Point size range: 1 to 256 Extensions: ANGLE_instanced_arrays EXT_blend_minmax EXT_color_buffer_half_float EXT_float_blend EXT_frag_depth EXT_shader_texture_lod EXT_texture_filter_anisotropic WEBKIT_EXT_texture_filter_anisotropic EXT_sRGB KHR_parallel_shader_compile OES_element_index_uint OES_standard_derivatives OES_texture_float OES_texture_float_linear OES_texture_half_float OES_texture_half_float_linear OES_vertex_array_object WEBGL_color_buffer_float WEBGL_compressed_texture_s3tc WEBKIT_WEBGL_compressed_texture_s3tc WEBGL_compressed_texture_s3tc_srgb WEBGL_debug_renderer_info WEBGL_debug_shaders WEBGL_depth_texture WEBKIT_WEBGL_depth_texture WEBGL_lose_context WEBKIT_WEBGL_lose_context WEBGL_multi_draw Audio information System sample rate: 48000 Hz Output channels: 2 Output interpretation: speakers Supported decode formats: WebM Opus (audio/webm; codecs=opus) Ogg Opus (audio/ogg; codecs=opus) WebM Vorbis (audio/webm; codecs=vorbis) Ogg Vorbis (audio/ogg; codecs=vorbis) MPEG-4 AAC (audio/mp4; codecs=mp4a.40.5) MP3 (audio/mpeg) FLAC (audio/flac) PCM WAV (audio/wav; codecs=1) Supported encode formats: WebM Opus (audio/webm; codecs=opus) Video information Supported decode formats: WebM AV1 (video/webm; codecs=av01.0.00M.08) MP4 AV1 (video/mp4; codecs=av01.0.00M.08) WebM VP9 (video/webm; codecs=vp9) WebM VP8 (video/webm; codecs=vp8) Ogg Theora (video/ogg; codecs=theora) H.264 (video/mp4; codecs=avc1.42E01E) Supported encode formats: WebM VP9 (video/webm; codecs=vp9) WebM VP8 (video/webm; codecs=vp8)