LibGL+LibSoftGPU: Implement viewport support

This implements the `glViewport` API call, the coordinate
transformation and the `GL_VIEWPORT` context parameter.

Userland/Libraries/LibGL/SoftwareGLContext.cpp

@@ -56,7 +56,8 @@ static constexpr size_t TEXTURE_MATRIX_STACK_LIMIT = 8;
     }
 
 SoftwareGLContext::SoftwareGLContext(Gfx::Bitmap& frontbuffer)
-    : m_frontbuffer(frontbuffer)
+    : m_viewport(frontbuffer.rect())
+    , m_frontbuffer(frontbuffer)
     , m_rasterizer(frontbuffer.size())
     , m_device_info(m_rasterizer.info())
 {
@@ -159,6 +160,18 @@ Optional<ContextParameter> SoftwareGLContext::get_context_parameter(GLenum name)
         return ContextParameter { .type = GL_INT, .value = { .integer_value = 0 } };
     case GL_UNPACK_SWAP_BYTES:
         return ContextParameter { .type = GL_BOOL, .value = { .boolean_value = false } };
+    case GL_VIEWPORT:
+        return ContextParameter {
+            .type = GL_INT,
+            .count = 4,
+            .value = {
+                .integer_list = {
+                    m_viewport.x(),
+                    m_viewport.y(),
+                    m_viewport.width(),
+                    m_viewport.height(),
+                } }
+        };
     default:
         dbgln_if(GL_DEBUG, "get_context_parameter({:#x}): unknown context parameter", name);
         return {};
@@ -577,11 +590,13 @@ void SoftwareGLContext::gl_viewport(GLint x, GLint y, GLsizei width, GLsizei hei
     APPEND_TO_CALL_LIST_AND_RETURN_IF_NEEDED(gl_viewport, x, y, width, height);
 
     RETURN_WITH_ERROR_IF(m_in_draw_state, GL_INVALID_OPERATION);
+    RETURN_WITH_ERROR_IF(width < 0 || height < 0, GL_INVALID_VALUE);
 
-    (void)(x);
-    (void)(y);
-    (void)(width);
-    (void)(height);
+    m_viewport = { x, y, width, height };
+
+    auto rasterizer_options = m_rasterizer.options();
+    rasterizer_options.viewport = m_viewport;
+    m_rasterizer.set_options(rasterizer_options);
 }
 
 void SoftwareGLContext::gl_enable(GLenum capability)

Userland/Libraries/LibGL/SoftwareGLContext.h

@@ -179,6 +179,8 @@ private:
     // FIXME: implement multi-texturing: the texture matrix stack should live inside a texture unit
     Vector<FloatMatrix4x4> m_texture_matrix_stack;
 
+    Gfx::IntRect m_viewport;
+
     FloatVector4 m_clear_color { 0.0f, 0.0f, 0.0f, 0.0f };
     double m_clear_depth { 1.0 };
     GLint m_clear_stencil { 0 };

Userland/Libraries/LibSoftGPU/Device.cpp

@@ -468,6 +468,7 @@ Device::Device(const Gfx::IntSize& size)
     , m_depth_buffer { adopt_own(*new DepthBuffer(size)) }
 {
     m_options.scissor_box = m_render_target->rect();
+    m_options.viewport = m_render_target->rect();
 }
 
 DeviceInfo Device::info() const
@@ -561,9 +562,6 @@ void Device::draw_primitives(PrimitiveType primitive_type, FloatMatrix4x4 const&
 
     m_enabled_texture_units = enabled_texture_units;
 
-    float scr_width = m_render_target->width();
-    float scr_height = m_render_target->height();
-
     m_triangle_list.clear_with_capacity();
     m_processed_triangles.clear_with_capacity();
 
@@ -621,6 +619,11 @@ void Device::draw_primitives(PrimitiveType primitive_type, FloatMatrix4x4 const&
     }
 
     // Now let's transform each triangle and send that to the GPU
+    auto const viewport = window_coordinates_to_target_coordinates(m_options.viewport, m_render_target->rect());
+    auto const viewport_half_width = viewport.width() / 2.0f;
+    auto const viewport_half_height = viewport.height() / 2.0f;
+    auto const viewport_center_x = viewport.x() + viewport_half_width;
+    auto const viewport_center_y = viewport.y() + viewport_half_height;
     auto const depth_half_range = (m_options.depth_max - m_options.depth_min) / 2;
     auto const depth_halfway = (m_options.depth_min + m_options.depth_max) / 2;
     for (auto& triangle : m_triangle_list) {
@@ -663,12 +666,11 @@ void Device::draw_primitives(PrimitiveType primitive_type, FloatMatrix4x4 const&
                 one_over_w,
             };
 
-            // To window coordinates
-            // FIXME: implement viewport functionality
+            // To window coordinates - note that we flip the Y coordinate into target space
             vec.window_coordinates = {
-                scr_width / 2 + ndc_coordinates.x() * scr_width / 2,
-                scr_height / 2 - ndc_coordinates.y() * scr_height / 2,
-                depth_half_range * ndc_coordinates.z() + depth_halfway,
+                viewport_center_x + ndc_coordinates.x() * viewport_half_width,
+                viewport_center_y - ndc_coordinates.y() * viewport_half_height,
+                depth_halfway + ndc_coordinates.z() * depth_half_range,
                 ndc_coordinates.w(),
             };
         }

Userland/Libraries/LibSoftGPU/Device.h

@@ -66,6 +66,7 @@ struct RasterizerOptions {
     bool cull_front { false };
     u8 texcoord_generation_enabled_coordinates { TexCoordGenerationCoordinate::None };
     Array<TexCoordGenerationConfig, 4> texcoord_generation_config {};
+    Gfx::IntRect viewport;
 };
 
 struct PixelQuad;