UI: Speed up icon scaling

Use GPU-side scaling to speed up the scaling itself, and to avoid having
to copy the image buffer using the CPU. Mipmapping is used to get decent
filtering when downscaling without ugly artifacts.
In my comparisons, there was barely any difference between the methods
for DPIs >= 1. Below that, the result looks a bit different due to the
different filtering method.

See D13144 for screen-recordings showing the difference.

Part of T92922.

Differential Revision: https://developer.blender.org/D13144

Reviewed by: Jeroen Bakker

source/blender/editors/include/BIF_glutil.h

@@ -54,6 +54,36 @@ typedef struct IMMDrawPixelsTexState {
  */
 IMMDrawPixelsTexState immDrawPixelsTexSetup(int builtin);
 
+/**
+ * Unlike the other `immDrawPixelsTex` functions, this doesn't do tiled drawing, but draws into a
+ * full texture.
+ *
+ * Use the currently bound shader.
+ *
+ * Use #immDrawPixelsTexSetup to bind the shader you want before calling #immDrawPixelsTex.
+ *
+ * If using a special shader double check it uses the same attributes "pos" "texCoord" and uniform
+ * "image".
+ *
+ * If color is NULL then use white by default
+ *
+ * Unless <em>state->do_shader_unbind<em> is explicitly set to `false`, the shader is unbound when
+ * finished.
+ */
+void immDrawPixelsTexScaledFullSize(const IMMDrawPixelsTexState *state,
+                                    const float x,
+                                    const float y,
+                                    const int img_w,
+                                    const int img_h,
+                                    const eGPUTextureFormat gpu_format,
+                                    const bool use_filter,
+                                    const void *rect,
+                                    const float scaleX,
+                                    const float scaleY,
+                                    const float xzoom,
+                                    const float yzoom,
+                                    const float color[4]);
+
 /**
  * #immDrawPixelsTex - Functions like a limited #glDrawPixels, but actually draws the
  * image using textures, which can be tremendously faster on low-end

source/blender/editors/interface/interface_icons.c

@@ -1546,7 +1546,7 @@ static void icon_draw_rect_fast(float x,
     immUniform1f("factor", desaturate);
   }
 
-  immDrawPixelsTexScaled(
+  immDrawPixelsTexScaledFullSize(
       &state, draw_x, draw_y, rw, rh, GPU_RGBA8, true, rect, scale_x, scale_y, 1.0f, 1.0f, col);
 }
 
@@ -1561,7 +1561,6 @@ static void icon_draw_rect(float x,
                            float alpha,
                            const float desaturate)
 {
-  ImBuf *ima = NULL;
   int draw_w = w;
   int draw_h = h;
   int draw_x = x;
@@ -1577,6 +1576,8 @@ static void icon_draw_rect(float x,
   /* modulate color */
   const float col[4] = {alpha, alpha, alpha, alpha};
 
+  float scale_x = 1.0f;
+  float scale_y = 1.0f;
   /* rect contains image in 'rendersize', we only scale if needed */
   if (rw != w || rh != h) {
     /* preserve aspect ratio and center */
@@ -1590,13 +1591,9 @@ static void icon_draw_rect(float x,
       draw_h = h;
       draw_x += (w - draw_w) / 2;
     }
+    scale_x = draw_w / (float)rw;
+    scale_y = draw_h / (float)rh;
     /* If the image is squared, the `draw_*` initialization values are good. */
-
-    /* first allocate imbuf for scaling and copy preview into it */
-    ima = IMB_allocImBuf(rw, rh, 32, IB_rect);
-    memcpy(ima->rect, rect, rw * rh * sizeof(uint));
-    IMB_scaleImBuf(ima, draw_w, draw_h); /* scale it */
-    rect = ima->rect;
   }
 
   /* draw */
@@ -1613,12 +1610,8 @@ static void icon_draw_rect(float x,
     immUniform1f("factor", desaturate);
   }
 
-  immDrawPixelsTex(
-      &state, draw_x, draw_y, draw_w, draw_h, GPU_RGBA8, false, rect, 1.0f, 1.0f, col);
-
-  if (ima) {
-    IMB_freeImBuf(ima);
-  }
+  immDrawPixelsTexScaledFullSize(
+      &state, draw_x, draw_y, rw, rh, GPU_RGBA8, true, rect, scale_x, scale_y, 1.0f, 1.0f, col);
 }
 
 /* High enough to make a difference, low enough so that

source/blender/editors/screen/glutil.c

@@ -72,6 +72,75 @@ IMMDrawPixelsTexState immDrawPixelsTexSetup(int builtin)
   return state;
 }
 
+void immDrawPixelsTexScaledFullSize(const IMMDrawPixelsTexState *state,
+                                    const float x,
+                                    const float y,
+                                    const int img_w,
+                                    const int img_h,
+                                    const eGPUTextureFormat gpu_format,
+                                    const bool use_filter,
+                                    const void *rect,
+                                    const float scaleX,
+                                    const float scaleY,
+                                    const float xzoom,
+                                    const float yzoom,
+                                    const float color[4])
+{
+  const static float white[4] = {1.0f, 1.0f, 1.0f, 1.0f};
+  const float draw_width = img_w * scaleX * xzoom;
+  const float draw_height = img_h * scaleY * yzoom;
+  /* Downscaling with regular bilinear interpolation (i.e. #GL_LINEAR) doesn't give good filtering
+   * results. Mipmaps can be used to get better results (i.e. #GL_LINEAR_MIPMAP_LINEAR), so always
+   * use mipmaps when filtering. */
+  const bool use_mipmap = use_filter && ((draw_width < img_w) || (draw_height < img_h));
+
+  GPUTexture *tex = GPU_texture_create_2d("immDrawPixels", img_w, img_h, 1, gpu_format, NULL);
+
+  const bool use_float_data = ELEM(gpu_format, GPU_RGBA16F, GPU_RGB16F, GPU_R16F);
+  eGPUDataFormat gpu_data_format = (use_float_data) ? GPU_DATA_FLOAT : GPU_DATA_UBYTE;
+  GPU_texture_update(tex, gpu_data_format, rect);
+
+  GPU_texture_filter_mode(tex, use_filter);
+  if (use_mipmap) {
+    GPU_texture_generate_mipmap(tex);
+    GPU_texture_mipmap_mode(tex, true, true);
+  }
+  GPU_texture_wrap_mode(tex, false, true);
+
+  GPU_texture_bind(tex, 0);
+
+  /* optional */
+  /* NOTE: Shader could be null for GLSL OCIO drawing, it is fine, since
+   * it does not need color.
+   */
+  if (state->shader != NULL && GPU_shader_get_uniform(state->shader, "color") != -1) {
+    immUniformColor4fv((color) ? color : white);
+  }
+
+  uint pos = state->pos, texco = state->texco;
+
+  immBegin(GPU_PRIM_TRI_FAN, 4);
+  immAttr2f(texco, 0.0f, 0.0f);
+  immVertex2f(pos, x, y);
+
+  immAttr2f(texco, 1.0f, 0.0f);
+  immVertex2f(pos, x + draw_width, y);
+
+  immAttr2f(texco, 1.0f, 1.0f);
+  immVertex2f(pos, x + draw_width, y + draw_height);
+
+  immAttr2f(texco, 0.0f, 1.0f);
+  immVertex2f(pos, x, y + draw_height);
+  immEnd();
+
+  if (state->do_shader_unbind) {
+    immUnbindProgram();
+  }
+
+  GPU_texture_unbind(tex);
+  GPU_texture_free(tex);
+}
+
 void immDrawPixelsTexScaled_clipping(IMMDrawPixelsTexState *state,
                                      float x,
                                      float y,