wined3d: Emulate fractional viewports if GL doesn't support them.

dlls/wined3d/adapter_gl.c

@@ -991,6 +991,7 @@ static void quirk_broken_arb_fog(struct wined3d_gl_info *gl_info)
 
 static void quirk_broken_viewport_subpixel_bits(struct wined3d_gl_info *gl_info)
 {
+    gl_info->limits.viewport_subpixel_bits = 0;
     if (gl_info->supported[ARB_CLIP_CONTROL])
     {
         TRACE("Disabling ARB_clip_control.\n");
@@ -3655,6 +3656,7 @@ static BOOL wined3d_adapter_init_gl_caps(struct wined3d_adapter *adapter,
             TRACE("Disabling ARB_clip_control because viewport subpixel bits < 8.\n");
             gl_info->supported[ARB_CLIP_CONTROL] = FALSE;
         }
+        gl_info->limits.viewport_subpixel_bits = subpixel_bits;
     }
     if (gl_info->supported[ARB_CLIP_CONTROL] && !gl_info->supported[ARB_VIEWPORT_ARRAY])
     {
@@ -5141,6 +5143,7 @@ static void wined3d_adapter_gl_init_d3d_info(struct wined3d_adapter_gl *adapter_
     d3d_info->full_ffp_varyings = !!(shader_caps.wined3d_caps & WINED3D_SHADER_CAP_FULL_FFP_VARYINGS);
     d3d_info->scaled_resolve = !!gl_info->supported[EXT_FRAMEBUFFER_MULTISAMPLE_BLIT_SCALED];
     d3d_info->pbo = !!gl_info->supported[ARB_PIXEL_BUFFER_OBJECT];
+    d3d_info->subpixel_viewport = gl_info->limits.viewport_subpixel_bits >= 8;
     d3d_info->feature_level = feature_level_from_caps(gl_info, &shader_caps, &fragment_caps);
     d3d_info->filling_convention_offset = gl_info->filling_convention_offset;
 

dlls/wined3d/adapter_vk.c

@@ -2257,6 +2257,7 @@ static void wined3d_adapter_vk_init_d3d_info(struct wined3d_adapter_vk *adapter_
     d3d_info->scaled_resolve = false;
     d3d_info->pbo = true;
     d3d_info->feature_level = feature_level_from_caps(&shader_caps);
+    d3d_info->subpixel_viewport = true;
 
     /* Like GL, Vulkan doesn't explicitly specify a filling convention and only mandates that a
      * shared edge of two adjacent triangles generate a fragment for exactly one of the triangles.

dlls/wined3d/state.c

@@ -4208,6 +4208,22 @@ static void viewport_miscpart(struct wined3d_context *context, const struct wine
             viewports[i * 4 + 1] = vp[i].y;
             viewports[i * 4 + 2] = vp[i].width;
             viewports[i * 4 + 3] = vp[i].height;
+
+            /* Don't pass fractionals to GL if we earlier decided not to use
+             * this functionality for two reasons: First, GL might offer us
+             * fewer than 8 bits, and still make use of the fractional, in
+             * addition to the emulation we apply in shader_get_position_fixup.
+             * Second, even if GL tells us it has no subpixel precision (Mac OS!)
+             * it might still do something with the fractional amount, e.g.
+             * round it upwards. I can't find any info on rounding in
+             * GL_ARB_viewport_array. */
+            if (!context->d3d_info->subpixel_viewport)
+            {
+                viewports[i * 4]     = floor(viewports[i * 4]);
+                viewports[i * 4 + 1] = floor(viewports[i * 4 + 1]);
+                viewports[i * 4 + 2] = floor(viewports[i * 4 + 2]);
+                viewports[i * 4 + 3] = floor(viewports[i * 4 + 3]);
+            }
         }
 
         if (context->viewport_count > state->viewport_count)

dlls/wined3d/wined3d_private.h

@@ -240,6 +240,7 @@ struct wined3d_d3d_info
     uint32_t full_ffp_varyings : 1;
     uint32_t scaled_resolve : 1;
     uint32_t pbo : 1;
+    uint32_t subpixel_viewport : 1;
     enum wined3d_feature_level feature_level;
 
     DWORD multisample_draw_location;
@@ -3237,6 +3238,7 @@ struct wined3d_gl_limits
 
     unsigned int framebuffer_width;
     unsigned int framebuffer_height;
+    unsigned int viewport_subpixel_bits;
 
     UINT glsl_varyings;
     UINT glsl_vs_float_constants;
@@ -5771,7 +5773,7 @@ static inline BOOL shader_is_scalar(const struct wined3d_shader_register *reg)
 static inline void shader_get_position_fixup(const struct wined3d_context *context,
         const struct wined3d_state *state, unsigned int fixup_count, float *position_fixup)
 {
-    float center_offset;
+    float center_offset, x = 0.0f, y = 0.0f;
     unsigned int i;
 
     /* See get_projection_matrix() in utils.c for a discussion of the position fixup.
@@ -5788,8 +5790,14 @@ static inline void shader_get_position_fixup(const struct wined3d_context *conte
     {
         position_fixup[4 * i    ] = 1.0f;
         position_fixup[4 * i + 1] = 1.0f;
-        position_fixup[4 * i + 2] = center_offset / state->viewports[i].width;
-        position_fixup[4 * i + 3] = -center_offset / state->viewports[i].height;
+        if (!context->d3d_info->subpixel_viewport)
+        {
+            double dummy;
+            x = modf(state->viewports[i].x, &dummy) * 2.0f;
+            y = modf(state->viewports[i].y, &dummy) * 2.0f;
+        }
+        position_fixup[4 * i + 2] = (center_offset + x) / state->viewports[i].width;
+        position_fixup[4 * i + 3] = -(center_offset + y) / state->viewports[i].height;
 
         if (context->render_offscreen)
         {