I also had the same issue. However I changed the code to leverage the built in OpenGL mipmap based downscaling to help with the look of downscaled images. It works kinda nicely as far as I have tested it.

I've attached the patch file.

diff --git a/src/canvas.c b/src/canvas.c index 2710efd..bae6df2 100644 --- a/src/canvas.c +++ b/src/canvas.c @@ -174,10 +167,14 @@ void imv_canvas_draw(struct imv_canvas *canvas) glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); glBegin(GL_TRIANGLE_FAN);

• glTexCoord2i(0, 0); glVertex2i(0.0, 0.0);
• glTexCoord2i(canvas->width, 0); glVertex2i(1.0, 0.0);
• glTexCoord2i(canvas->width, canvas->height); glVertex2i(1.0, 1.0);
• glTexCoord2i(0, canvas->height); glVertex2i(0.0, 1.0);

• glTexCoord2i(0, 0);
• glVertex2i(0.0, 0.0);
• glTexCoord2i(canvas->width, 0);
• glVertex2i(1.0, 0.0);
• glTexCoord2i(canvas->width, canvas->height);
• glVertex2i(1.0, 1.0);
• glTexCoord2i(0, canvas->height);
• glVertex2i(0.0, 1.0); glEnd(); glDisable(GL_BLEND);

@@ -222,7 +215,7 @@ static void draw_bitmap(struct imv_canvas *canvas,

const int format = convert_pixelformat(bitmap->format);

• glBindTexture(GL_TEXTURE_RECTANGLE, canvas->cache.texture);

• glBindTexture(GL_TEXTURE_2D, canvas->cache.texture);

  GLint upscaling = 0; if (upscaling_method == UPSCALING_LINEAR) { @@ -235,19 +228,21 @@ static void draw_bitmap(struct imv_canvas *canvas, }

  if (canvas->cache.bitmap != bitmap || cache_invalidated) {

• glTexParameteri(GL_TEXTURE_RECTANGLE, GL_TEXTURE_MIN_FILTER, upscaling);
• glTexParameteri(GL_TEXTURE_RECTANGLE, GL_TEXTURE_MAG_FILTER, upscaling);

• glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,

•                GL_LINEAR_MIPMAP_LINEAR);
  

• glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, upscaling); glPixelStorei(GL_UNPACK_ROW_LENGTH, bitmap->width); glPixelStorei(GL_UNPACK_SKIP_ROWS, 0); glPixelStorei(GL_UNPACK_SKIP_PIXELS, 0);

• glTexImage2D(GL_TEXTURE_RECTANGLE, 0, GL_RGBA8, bitmap->width, bitmap->height,

•    0, format, GL_UNSIGNED_INT_8_8_8_8_REV, bitmap->data);
  

• glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, bitmap->width, bitmap->height, 0,

•             format, GL_UNSIGNED_INT_8_8_8_8_REV, bitmap->data);
  

• glGenerateMipmap(GL_TEXTURE_2D); } canvas->cache.bitmap = bitmap;

• glEnable(GL_TEXTURE_RECTANGLE);

• glEnable(GL_TEXTURE_2D);

• glTexParameteri(GL_TEXTURE_RECTANGLE, GL_TEXTURE_MAG_FILTER, upscaling);

• glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, upscaling);

  const int left = bx; const int top = by; @@ -267,16 +262,20 @@ static void draw_bitmap(struct imv_canvas *canvas, glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

  glBegin(GL_TRIANGLE_FAN);

• glTexCoord2i(0, 0); glVertex2i(left, top);
• glTexCoord2i(bitmap->width, 0); glVertex2i(right, top);
• glTexCoord2i(bitmap->width, bitmap->height); glVertex2i(right, bottom);
• glTexCoord2i(0, bitmap->height); glVertex2i(left, bottom);

• glTexCoord2i(0, 0);

• glVertex2i(left, top);

• glTexCoord2i(1, 0);

• glVertex2i(right, top);

• glTexCoord2i(1, 1);

• glVertex2i(right, bottom);

• glTexCoord2i(0, 1);

• glVertex2i(left, bottom); glEnd();

  glDisable(GL_BLEND);

• glBindTexture(GL_TEXTURE_RECTANGLE, 0);
• glDisable(GL_TEXTURE_RECTANGLE);

• glBindTexture(GL_TEXTURE_2D, 0);
• glDisable(GL_TEXTURE_2D); glPopMatrix(); }

Seems like there is no good way to attach files here without them getting mangled.. :/

Here is a gist with the patch file: https://gist.github.com/DarkDefender/7d8a53fd1a62f65461e42b32ec56ed67

On Fri, Jan 20, 2023 at 10:41:50PM +0000, Sebastian Parborg wrote:

I also had the same issue. However I changed the code to leverage the built in OpenGL mipmap based downscaling to help with the look of downscaled images. It works kinda nicely as far as I have tested it.

I've attached the patch file. Thank you Sebastian, It is not as good as eg gimp but looks much nicer... And if I understand correctly it is a way faster on GPU then computing it on CPU :)

I applied your patch and here the results for my sample image: https://skyboo.net/temp/imv/before.png https://skyboo.net/temp/imv/after.png

-- regards, Mariusz Białończyk https://skyboo.net | https://github.com/manio

So, is this happening?

What git commit of imv was this patch made for?