LibGL+LibGPU+LibSoftGPU: Implement flexible pixel format conversion

A GPU (driver) is now responsible for reading and writing pixels from
and to user data. The client (LibGL) is responsible for specifying how
the user data must be interpreted or written to.

This allows us to centralize all pixel format conversion in one class,
`LibSoftGPU::PixelConverter`. For both the input and output image, it
takes a specification containing the image dimensions, the pixel type
and the selection (basically a clipping rect), and converts the pixels
from the input image to the output image.

Effectively this means we now support almost all OpenGL 1.5 formats,
and all custom logic has disappeared from:
  - `glDrawPixels`
  - `glReadPixels`
  - `glTexImage2D`
  - `glTexSubImage2D`

The new logic is still unoptimized, but on my machine I experienced no
noticeable slowdown. :^)

1 files changed, 24 insertions, 0 deletions

diff --git a/Userland/Libraries/LibGL/ContextParameter.cpp b/Userland/Libraries/LibGL/ContextParameter.cpp
index 83a0326f29..c35048c7bd 100644
--- a/Userland/Libraries/LibGL/ContextParameter.cpp
+++ b/Userland/Libraries/LibGL/ContextParameter.cpp
@@ -584,4 +584,28 @@ GLboolean GLContext::gl_is_enabled(GLenum capability)
     return parameter.value.boolean_value;
 }
 
+GPU::PackingSpecification GLContext::get_packing_specification(PackingType packing_type)
+{
+    // Make use of the fact that the GL_PACK_* and GL_UNPACK_* enum constants are in the exact same order
+    auto const offset = (packing_type == PackingType::Unpack) ? 0 : (GL_PACK_SWAP_BYTES - GL_UNPACK_SWAP_BYTES);
+    auto get_packing_value = [&](GLenum packing_parameter) -> GLint {
+        GLint value;
+        gl_get_integerv(packing_parameter + offset, &value);
+        return value;
+    };
+
+    // FIXME: add support for GL_UNPACK_SKIP_PIXELS, GL_UNPACK_SKIP_ROWS and GL_UNPACK_LSB_FIRST
+    GLint byte_alignment { get_packing_value(GL_UNPACK_ALIGNMENT) };
+    GLint swap_bytes { get_packing_value(GL_UNPACK_SWAP_BYTES) };
+    GLint depth_stride { get_packing_value(GL_UNPACK_IMAGE_HEIGHT) };
+    GLint row_stride { get_packing_value(GL_UNPACK_ROW_LENGTH) };
+
+    return {
+        .depth_stride = static_cast<u32>(depth_stride),
+        .row_stride = static_cast<u32>(row_stride),
+        .byte_alignment = static_cast<u8>(byte_alignment),
+        .component_bytes_order = swap_bytes == GL_TRUE ? GPU::ComponentBytesOrder::Reversed : GPU::ComponentBytesOrder::Normal,
+    };
+}
+
 }