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Backends: Improve pixel blending and surface format conversion in SDL_Surface

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This commit is contained in:
moonpower 2025-12-25 00:25:31 +03:00
parent a59e03e1e7
commit eeb20d048b
1 changed files with 41 additions and 16 deletions
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57
backends/imgui_impl_sdlsurface2.cpp
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@ -33,26 +33,43 @@ static inline void BlendPixel(SDL_Surface* s, int x, int y,
if (!s || sa == 0) return;
if (x < 0 || y < 0 || x >= s->w || y >= s->h) return;
Uint32 dst_pix = GetPixel(s, x, y);
if (sa == 255)
{
Uint32 out_pix = SDL_MapRGBA(s->format, sr, sg, sb, sa);
Uint8* p = (Uint8*)s->pixels + y * s->pitch + x * s->format->BytesPerPixel;
switch (s->format->BytesPerPixel)
{
case 1: *p = (Uint8)out_pix; break;
case 2: *(Uint16*)p = (Uint16)out_pix; break;
case 3:
if (SDL_BYTEORDER == SDL_BIG_ENDIAN)
{
p[0] = (out_pix >> 16) & 0xFF;
p[1] = (out_pix >> 8) & 0xFF;
p[2] = out_pix & 0xFF;
}
else
{
p[0] = out_pix & 0xFF;
p[1] = (out_pix >> 8) & 0xFF;
p[2] = (out_pix >> 16) & 0xFF;
}
break;
case 4: *(Uint32*)p = out_pix; break;
}
return;
}
Uint32 dst_pix = GetPixel(s, x, y);
Uint8 dr, dg, db, da;
SDL_GetRGBA(dst_pix, s->format, &dr, &dg, &db, &da);
float src_a = sa / 255.0f;
float dst_a = da / 255.0f;
float out_a = src_a + dst_a * (1.0f - src_a);
float out_r = (sr * src_a + dr * dst_a * (1.0f - src_a)) / (out_a > 0 ? out_a : 1.0f);
float out_g = (sg * src_a + dg * dst_a * (1.0f - src_a)) / (out_a > 0 ? out_a : 1.0f);
float out_b = (sb * src_a + db * dst_a * (1.0f - src_a)) / (out_a > 0 ? out_a : 1.0f);
Uint8 fr = (Uint8)std::clamp(out_r, 0.0f, 255.0f);
Uint8 fg = (Uint8)std::clamp(out_g, 0.0f, 255.0f);
Uint8 fb = (Uint8)std::clamp(out_b, 0.0f, 255.0f);
Uint8 fa = (Uint8)std::clamp(out_a * 255.0f, 0.0f, 255.0f);
Uint32 out_pix = SDL_MapRGBA(s->format, fr, fg, fb, fa);
Uint8 out_r = (Uint8)((sr * sa + dr * (255 - sa)) / 255);
Uint8 out_g = (Uint8)((sg * sa + dg * (255 - sa)) / 255);
Uint8 out_b = (Uint8)((sb * sa + db * (255 - sa)) / 255);
Uint8 out_a = (Uint8)((sa + (da * (255 - sa)) / 255));
Uint32 out_pix = SDL_MapRGBA(s->format, out_r, out_g, out_b, out_a);
Uint8* p = (Uint8*)s->pixels + y * s->pitch + x * s->format->BytesPerPixel;
switch (s->format->BytesPerPixel)
{
@ -103,10 +120,18 @@ bool ImGui_ImplSDLSurface2_Init(SDL_Surface* surface)
{
if (!surface) return false;
g_TargetSurface = surface;
g_FontSurface = ImGui_ImplSDLSurface2_CreateFontAtlasSurface();
if (g_FontSurface)
{
if (g_TargetSurface && g_FontSurface->format->format != g_TargetSurface->format->format)
{
SDL_Surface* converted = SDL_ConvertSurfaceFormat(g_FontSurface, g_TargetSurface->format->format, 0);
if (converted)
{
SDL_FreeSurface(g_FontSurface);
g_FontSurface = converted;
}
}
ImGui::GetIO().Fonts->TexID = (ImTextureID)g_FontSurface;
}
return true;