mesa: fix _FP32Buffers bitfield use

Previously we were assuming that all color attachments were active.

Fixes: 070a5e5d92 ("mesa: add explicit enable for EXT_float_blend, and error condition")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35014>

src/mesa/main/buffers.c

@@ -764,6 +764,8 @@ _mesa_update_drawbuffer_masks(struct gl_context *ctx,
                           &ctx->DrawBuffer->_BlendForceAlphaToOneDraw);
    update_drawbuffer_mask(ctx, fb, &ctx->DrawBuffer->_IsRGB,
                           &ctx->DrawBuffer->_IsRGBDraw);
+   update_drawbuffer_mask(ctx, fb, &ctx->DrawBuffer->_FP32Buffers,
+                          &ctx->DrawBuffer->_FP32DrawBuffers);
 }
 
 /**

src/mesa/main/draw_validate.c

@@ -234,7 +234,7 @@ _mesa_update_valid_to_render_state(struct gl_context *ctx)
        * However GL_EXT_float_blend removes this text.
        */
       if (!ctx->Extensions.EXT_float_blend &&
-          (ctx->DrawBuffer->_FP32Buffers & ctx->Color.BlendEnabled))
+          (ctx->DrawBuffer->_FP32DrawBuffers & ctx->Color.BlendEnabled))
          return;
       break;
 

src/mesa/main/mtypes.h

@@ -2697,7 +2697,8 @@ struct gl_framebuffer
    GLbitfield _BlendForceAlphaToOneDraw;  /**< Which color buffers need blend factor adjustment */
    GLbitfield _IsRGB;  /**< Which color attachments have an RGB base format? */
    GLbitfield _IsRGBDraw;  /**< Which color buffers have an RGB base format? */
-   GLbitfield _FP32Buffers; /**< Which color buffers are FP32 */
+   GLbitfield _FP32Buffers; /**< Which color attachments are FP32 */
+   GLbitfield _FP32DrawBuffers; /**< Which color buffers are FP32 */
 
    /* ARB_color_buffer_float */
    GLboolean _AllColorBuffersFixedPoint; /* no integer, no float */