API Reference

Class TRenderContext

Description
Hierarchy
Fields
Methods
Properties

Unit

CastleRenderContext

Declaration

type TRenderContext = class(TComponent)

Description

The OpenGL / OpenGLES context state. We try hard to make this a very, very small class, because usually it's better to introduce a clean higher-level API than to track the OpenGL context state in a simple global RenderContext instance.

Use the methods and properties of this class only when this context is current, which means it's set as RenderContext value.

Do not depend on the context state being persistent. The RenderContext does not change during a single TCastleUserInterface.OnRender method (with all 2D and 3D stuff rendered inside), but that's all we guarantee. On desktops, you control the context creation / destruction explicitly (by opening / closing the TCastleWindow). But on mobile devices – the context may get destroyed and created at almost any moment. So do not use the instance of RenderContext to store anything you rely on being stored. Instead, use your own variables for this, and only synchronize RenderContext with your variables.

Hierarchy

  • TObject
  • TPersistent
  • TComponent
  • TRenderContext

Overview

Fields

Public InternalClearColorsByDraw: Boolean;

Methods

Public constructor Create(AOwner: TComponent); override;
Public destructor Destroy; override;
Public procedure Clear(Buffers: TClearBuffers; const ClearColor: TCastleColor);
Public procedure ScissorEnable(const Rect: TRectangle);
Public procedure ScissorDisable;
Public function FinalScissor(out Rect: TRectangle): Boolean;
Public function ColorBufferHasAlpha: Boolean; deprecated 'use GLFeatures.AlphaBits > 0';
Public procedure BlendingEnable( const SourceFactor: TBlendingSourceFactor = bsSrcAlpha; const DestinationFactor: TBlendingDestinationFactor = bdOneMinusSrcAlpha);
Public procedure BlendingDisable;
Public procedure FixedFunctionAlphaTestEnable(const AlphaCutoff: Single = 0.5);
Public procedure FixedFunctionAlphaTestDisable;
Public procedure PolygonOffsetEnable(const Scale, Bias: Single);
Public procedure PolygonOffsetDisable;

Properties

Public property LineWidth: Single read FLineWidth write SetLineWidth default 1;
Public property PointSize: Single read FPointSize write SetPointSize default 1;
Public property GlobalAmbient: TCastleColorRGB read FGlobalAmbient write SetGlobalAmbient;
Public property ProjectionMatrix: TMatrix4 read FProjectionMatrix write SetProjectionMatrix;
Public property DepthRange: TDepthRange read FDepthRange write SetDepthRange;
Public property CullFace: boolean read FCullFace write SetCullFace default false;
Public property FrontFaceCcw: boolean read FFrontFaceCcw write SetFrontFaceCcw default true;
Public property DepthTest: Boolean read FDepthTest write SetDepthTest default false;
Public property DepthFunc: TDepthFunction read FDepthFunc write SetDepthFunc default dfLess;
Public property ColorMask: boolean read GetColorMask write SetColorMask default true; deprecated 'use ColorChannels';
Public property ColorChannels: TColorChannels read FColorChannels write SetColorChannels default AllColorChannels;
Public property DepthBufferUpdate: Boolean read FDepthBufferUpdate write SetDepthBufferUpdate default true;
Public property Viewport: TRectangle read FViewport write SetViewport;
Public property ViewportDelta: TVector2Integer read FViewportDelta write SetViewportDelta;
Public property CurrentProgram: TGLSLProgram read FCurrentProgram write SetCurrentProgram;
Public property CurrentVao: TVertexArrayObject read FCurrentVao write SetCurrentVao;
Public property FixedFunctionLighting: boolean read FFixedFunctionLighting write SetFixedFunctionLighting;
Public property LineType: TLineType read FLineType write SetLineType;
Public property PolygonOffset: TPolygonOffset read FPolygonOffset write SetPolygonOffset;
Public property BindBuffer[const Target: TBufferTarget]: TGLuint read GetBoundBuffer write SetBoundBuffer;

Description

Fields

Public InternalClearColorsByDraw: Boolean;

If True, Clear will clear color buffer by DrawRectangle instead of OpenGL glClear call. This is a bit slower, but makes it honor the stencil test.

Methods

Public constructor Create(AOwner: TComponent); override;

This item has no description.

Public destructor Destroy; override;

This item has no description.

Public procedure Clear(Buffers: TClearBuffers; const ClearColor: TCastleColor);

Clear the whole buffer contents.

Never call OpenGL glClear or glClearColor, always use this method.

Public procedure ScissorEnable(const Rect: TRectangle);

Enable or disable scissor.

Never call OpenGL glScissor or glEnable(GL_SCISSOR_TEST) / glDisable(GL_SCISSOR_TEST) directly, or push/pop the related attrib (in case of fixed-function pipeline).

Public procedure ScissorDisable;

This item has no description.

Public function FinalScissor(out Rect: TRectangle): Boolean;

Scissor rectangle to which we clip the view. This is determined by all TScissor that are currently enabled. Returns True and sets Rect if any scissor is active. Returns False if we don't clip the view now.

Public function ColorBufferHasAlpha: Boolean; deprecated 'use GLFeatures.AlphaBits > 0';

Warning: this symbol is deprecated: use GLFeatures.AlphaBits > 0

Does the current color buffer have any alpha channel. Some blending features depend on storing alpha in the color channel.

Public procedure BlendingEnable( const SourceFactor: TBlendingSourceFactor = bsSrcAlpha; const DestinationFactor: TBlendingDestinationFactor = bdOneMinusSrcAlpha);

Enable blending, sets also blending function. See https://registry.khronos.org/OpenGL-Refpages/gl4/html/glBlendFunc.xhtml for blending equations. You must use this to change blending parameters, this class assumes it knows the blending state always.

Public procedure BlendingDisable;

This item has no description.

Public procedure FixedFunctionAlphaTestEnable(const AlphaCutoff: Single = 0.5);

Enable alpha test with old/buggy OpenGL implementations that use deprecated fixed-function pipeline. This is simply ignored on modern GPUs when "not GLFeatures.EnableFixedFunction".

Public procedure FixedFunctionAlphaTestDisable;

This item has no description.

Public procedure PolygonOffsetEnable(const Scale, Bias: Single);

Shortcut for setting PolygonOffset with PolygonOffset.Enabled = True.

Public procedure PolygonOffsetDisable;

Shortcut for setting PolygonOffset with PolygonOffset.Enabled = False.

Properties

Public property LineWidth: Single read FLineWidth write SetLineWidth default 1;

The rendered line width. Never call OpenGL glLineWidth directly.

Do not access this property directly, unless you make direct OpenGL/OpenGLES calls. In normal circumstances, engine API (like DrawPrimitive2D or TCastleScene) set this automatically.

Public property PointSize: Single read FPointSize write SetPointSize default 1;

The rendered point size. Never call OpenGL glPointSize directly.

Do not access this property directly, unless you make direct OpenGL/OpenGLES calls. In normal circumstances, engine API (like DrawPrimitive2D or TCastleScene) set this automatically.

Public property GlobalAmbient: TCastleColorRGB read FGlobalAmbient write SetGlobalAmbient;

Global ambient lighting. This is added to every 3D object color, multiplied by material ambient.

The default value is (0.2, 0.2, 0.2). It matches default GL_LIGHT_MODEL_AMBIENT in fixed-function OpenGL. It also matches the required value of VRML 1.0 specification. For VRML 2.0 / X3D, lighting equations suggest that it should be zero.

Public property ProjectionMatrix: TMatrix4 read FProjectionMatrix write SetProjectionMatrix;

Current projection matrix.

When GLFeatures.EnableFixedFunction = true, setting this also sets fixed-function projection matrix.

Public property DepthRange: TDepthRange read FDepthRange write SetDepthRange;

Use this to operate on OpenGL glDepthRange. For now, our engine has very simple use for this, for TPlayer.RenderOnTop.

Public property CullFace: boolean read FCullFace write SetCullFace default false;

Should we use backface-culling (ignore some faces during rendering).

Public property FrontFaceCcw: boolean read FFrontFaceCcw write SetFrontFaceCcw default true;

Is the front face ordered counter-clockwise. The "front face" is important to interpreting the CullFace and to interpret the normal vectors (they point outward from front face).

Public property DepthTest: Boolean read FDepthTest write SetDepthTest default false;

Depth testing means we reject things that don't pass DepthFunc.

Public property DepthFunc: TDepthFunction read FDepthFunc write SetDepthFunc default dfLess;

Function to use when comparing depth, only if DepthTest.

Public property ColorMask: boolean read GetColorMask write SetColorMask default true; deprecated 'use ColorChannels';

Warning: this symbol is deprecated: use ColorChannels

Are color buffer channels changed by rendering.

Public property ColorChannels: TColorChannels read FColorChannels write SetColorChannels default AllColorChannels;

Which color buffer channels are written by rendering. This affects all rendering, including TDrawableImage.Draw.

Note that this state may be internally modified by various engine rendering functions too, e.g. by TCastleScene.LocalRender, depending on rendering attributes. So it is only reliable for you to modify this temporarily, and during your own rendering. E.g. change ColorChannels right before and right after calling a couple of TDrawableImage.Draw. Always restore it afterwards to default [0..3].

Example uses:

  • Set this to ccNone to temporarily turn off writing to the color buffer. This is useful e.g. if you only want to write to the delph and stencil buffer.

  • Set this to [0..2] to temporarily turn off writing to the alpha channel, or to [3] to temporarily turn off writing to the RGB channels.

  • Set this [0..3] to go back to default (write all channels).

Public property DepthBufferUpdate: Boolean read FDepthBufferUpdate write SetDepthBufferUpdate default true;

Is depth buffer updated by rendering. This affects all rendering that enables depth testing (which in practice means only TCastleScene in CGE).

Public property Viewport: TRectangle read FViewport write SetViewport;

Controls OpenGL viewport. This is always shifted by ViewportDelta.

Public property ViewportDelta: TVector2Integer read FViewportDelta write SetViewportDelta;

Shifts the rectangle passed to Viewport. Only the TCastleScreenEffects should control this.

Public property CurrentProgram: TGLSLProgram read FCurrentProgram write SetCurrentProgram;

Currently enabled GLSL program. Nil if none (rendering is not possible, unless ancient fixed-function pipeline is used). Setting this property encapsulates the OpenGL glUseProgram.

Public property CurrentVao: TVertexArrayObject read FCurrentVao write SetCurrentVao;

Currently bound vertex array object. Nil if none..

Public property FixedFunctionLighting: boolean read FFixedFunctionLighting write SetFixedFunctionLighting;

Fixed-function GL_LIGHTING state. This is simply ignored on modern GPUs when "not GLFeatures.EnableFixedFunction".

Public property LineType: TLineType read FLineType write SetLineType;

Line type determines OpenGL glLineStipple, GL_LINE_STIPPLE enable state. Note: This is not supported on OpenGLES.

Public property PolygonOffset: TPolygonOffset read FPolygonOffset write SetPolygonOffset;

Current polygon offset state. You can read and write it.

Public property BindBuffer[const Target: TBufferTarget]: TGLuint read GetBoundBuffer write SetBoundBuffer;

Bind buffer to target, just like glBindBuffer.

Optimized to do nothing if given buffer is already bound. This optimization actually matters for optimization (Android Samsung Galaxy Tab, castle-model-viewer-mobile displaying inspector). Without it, TDrawableImage does a lot of redundant glBindBuffer calls.

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