meta: Add a GLSL-based _mesa_meta_Clear() variant.

This cuts out a large portion of the overhead of glClear() from
resetting the texenv state and recomputing the fixed function
programs.  It also means less use of fixed function internally in our
GLES2 drivers, which is rather bogus.

Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/drivers/common/meta.c

@@ -62,6 +62,7 @@
 #include "main/teximage.h"
 #include "main/texparam.h"
 #include "main/texstate.h"
+#include "main/uniforms.h"
 #include "main/varray.h"
 #include "main/viewport.h"
 #include "program/program.h"
@@ -235,6 +236,8 @@ struct clear_state
 {
    GLuint ArrayObj;
    GLuint VBO;
+   GLuint ShaderProg;
+   GLint ColorLocation;
 };
 
 
@@ -1589,10 +1592,165 @@ _mesa_meta_Clear(struct gl_context *ctx, GLbitfield buffers)
    _mesa_meta_end(ctx);
 }
 
+static void
+meta_glsl_clear_init(struct gl_context *ctx, struct clear_state *clear)
+{
+   const char *vs_source =
+      "attribute vec4 position;\n"
+      "void main()\n"
+      "{\n"
+      "   gl_Position = position;\n"
+      "}\n";
+   const char *fs_source =
+      "uniform vec4 color;\n"
+      "void main()\n"
+      "{\n"
+      "   gl_FragColor = color;\n"
+      "}\n";
+   GLuint vs, fs;
+
+   if (clear->ArrayObj != 0)
+      return;
+
+   /* create vertex array object */
+   _mesa_GenVertexArrays(1, &clear->ArrayObj);
+   _mesa_BindVertexArray(clear->ArrayObj);
+
+   /* create vertex array buffer */
+   _mesa_GenBuffersARB(1, &clear->VBO);
+   _mesa_BindBufferARB(GL_ARRAY_BUFFER_ARB, clear->VBO);
+
+   /* setup vertex arrays */
+   _mesa_VertexAttribPointerARB(0, 3, GL_FLOAT, GL_FALSE, 0, (void *)0);
+   _mesa_EnableVertexAttribArrayARB(0);
+
+   vs = _mesa_CreateShaderObjectARB(GL_VERTEX_SHADER);
+   _mesa_ShaderSourceARB(vs, 1, &vs_source, NULL);
+   _mesa_CompileShaderARB(vs);
+
+   fs = _mesa_CreateShaderObjectARB(GL_FRAGMENT_SHADER);
+   _mesa_ShaderSourceARB(fs, 1, &fs_source, NULL);
+   _mesa_CompileShaderARB(fs);
+
+   clear->ShaderProg = _mesa_CreateProgramObjectARB();
+   _mesa_AttachShader(clear->ShaderProg, fs);
+   _mesa_AttachShader(clear->ShaderProg, vs);
+   _mesa_BindAttribLocationARB(clear->ShaderProg, 0, "position");
+   _mesa_LinkProgramARB(clear->ShaderProg);
+
+   clear->ColorLocation = _mesa_GetUniformLocationARB(clear->ShaderProg,
+						      "color");
+}
+
+/**
+ * Meta implementation of ctx->Driver.Clear() in terms of polygon rendering.
+ */
+void
+_mesa_meta_glsl_Clear(struct gl_context *ctx, GLbitfield buffers)
+{
+   struct clear_state *clear = &ctx->Meta->Clear;
+   GLbitfield metaSave;
+   const GLuint stencilMax = (1 << ctx->DrawBuffer->Visual.stencilBits) - 1;
+   struct gl_framebuffer *fb = ctx->DrawBuffer;
+   const float x0 = ((float)fb->_Xmin / fb->Width)  * 2.0f - 1.0f;
+   const float y0 = ((float)fb->_Ymin / fb->Height) * 2.0f - 1.0f;
+   const float x1 = ((float)fb->_Xmax / fb->Width)  * 2.0f - 1.0f;
+   const float y1 = ((float)fb->_Ymax / fb->Height) * 2.0f - 1.0f;
+   const float z = -invert_z(ctx->Depth.Clear);
+   struct vertex {
+      GLfloat x, y, z;
+   } verts[4];
+
+   metaSave = (META_ALPHA_TEST |
+	       META_BLEND |
+	       META_DEPTH_TEST |
+	       META_RASTERIZATION |
+	       META_SHADER |
+	       META_STENCIL_TEST |
+	       META_VERTEX |
+	       META_VIEWPORT |
+	       META_CLAMP_FRAGMENT_COLOR);
+
+   if (!(buffers & BUFFER_BITS_COLOR)) {
+      /* We'll use colormask to disable color writes.  Otherwise,
+       * respect color mask
+       */
+      metaSave |= META_COLOR_MASK;
+   }
+
+   _mesa_meta_begin(ctx, metaSave);
+
+   meta_glsl_clear_init(ctx, clear);
+
+   _mesa_UseProgramObjectARB(clear->ShaderProg);
+   _mesa_Uniform4fvARB(clear->ColorLocation, 1,
+		       ctx->Color.ClearColorUnclamped);
+
+   _mesa_BindVertexArray(clear->ArrayObj);
+   _mesa_BindBufferARB(GL_ARRAY_BUFFER_ARB, clear->VBO);
+
+   /* GL_COLOR_BUFFER_BIT */
+   if (buffers & BUFFER_BITS_COLOR) {
+      /* leave colormask, glDrawBuffer state as-is */
+
+      /* Clears never have the color clamped. */
+      _mesa_ClampColorARB(GL_CLAMP_FRAGMENT_COLOR, GL_FALSE);
+   }
+   else {
+      ASSERT(metaSave & META_COLOR_MASK);
+      _mesa_ColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
+   }
+
+   /* GL_DEPTH_BUFFER_BIT */
+   if (buffers & BUFFER_BIT_DEPTH) {
+      _mesa_set_enable(ctx, GL_DEPTH_TEST, GL_TRUE);
+      _mesa_DepthFunc(GL_ALWAYS);
+      _mesa_DepthMask(GL_TRUE);
+   }
+   else {
+      assert(!ctx->Depth.Test);
+   }
+
+   /* GL_STENCIL_BUFFER_BIT */
+   if (buffers & BUFFER_BIT_STENCIL) {
+      _mesa_set_enable(ctx, GL_STENCIL_TEST, GL_TRUE);
+      _mesa_StencilOpSeparate(GL_FRONT_AND_BACK,
+                              GL_REPLACE, GL_REPLACE, GL_REPLACE);
+      _mesa_StencilFuncSeparate(GL_FRONT_AND_BACK, GL_ALWAYS,
+                                ctx->Stencil.Clear & stencilMax,
+                                ctx->Stencil.WriteMask[0]);
+   }
+   else {
+      assert(!ctx->Stencil.Enabled);
+   }
+
+   /* vertex positions */
+   verts[0].x = x0;
+   verts[0].y = y0;
+   verts[0].z = z;
+   verts[1].x = x1;
+   verts[1].y = y0;
+   verts[1].z = z;
+   verts[2].x = x1;
+   verts[2].y = y1;
+   verts[2].z = z;
+   verts[3].x = x0;
+   verts[3].y = y1;
+   verts[3].z = z;
+
+   /* upload new vertex data */
+   _mesa_BufferDataARB(GL_ARRAY_BUFFER_ARB, sizeof(verts), verts,
+		       GL_DYNAMIC_DRAW_ARB);
+
+   /* draw quad */
+   _mesa_DrawArrays(GL_TRIANGLE_FAN, 0, 4);
+
+   _mesa_meta_end(ctx);
+}
 
 /**
  * Meta implementation of ctx->Driver.CopyPixels() in terms
- * of texture mapping and polygon rendering.
+ * of texture mapping and polygon rendering and GLSL shaders.
  */
 void
 _mesa_meta_CopyPixels(struct gl_context *ctx, GLint srcX, GLint srcY,

src/mesa/drivers/common/meta.h

@@ -42,6 +42,9 @@ _mesa_meta_BlitFramebuffer(struct gl_context *ctx,
 extern void
 _mesa_meta_Clear(struct gl_context *ctx, GLbitfield buffers);
 
+extern void
+_mesa_meta_glsl_Clear(struct gl_context *ctx, GLbitfield buffers);
+
 extern void
 _mesa_meta_CopyPixels(struct gl_context *ctx, GLint srcx, GLint srcy,
                       GLsizei width, GLsizei height,