Drawbuffers

Macros
#define	oslGetDrawBuffer()   osl_curBuf
#define	OSL_DEFAULT_BUFFER   (&osl_defaultBufferImage)
#define	OSL_SECONDARY_BUFFER   (&osl_secondaryBufferImage)
#define	OSL_SCREEN_WIDTH   (osl_curBuf->sizeX)
#define	OSL_SCREEN_HEIGHT   (osl_curBuf->sizeY)

Enumerations
enum	OSL_FX_ALPHAWRITE { OSL_FXAW_NONE , OSL_FXAW_SET }
enum	OSL_FX_ALPHATEST {   OSL_FXAT_NEVER = GU_NEVER , OSL_FXAT_ALWAYS = GU_ALWAYS , OSL_FXAT_EQUAL = GU_EQUAL , OSL_FXAT_NOTEQUAL = GU_NOTEQUAL ,   OSL_FXAT_LESS = GU_LESS , OSL_FXAT_LEQUAL = GU_LEQUAL , OSL_FXAT_GREATER = GU_GREATER , OSL_FXAT_GEQUAL = GU_GEQUAL }

Functions
void	oslSetDrawBuffer (OSL_IMAGE *img)
void	oslSetAlphaWrite (int action, int value1, int value2)
	Controls writing to the alpha channel of the draw buffer.
void	oslSetAlphaTest (int condition, int value)
void	oslDisableAlphaTest ()

Variables
int	osl_alphaTestEnabled

Detailed Description

Drawbuffers is an advanced and powerful capability of OSLib images. It allows you to draw directly on an image exactly as if you were drawing on the screen! See oslSetDrawBuffer for a basic code sample.

Macro Definition Documentation

oslGetDrawBuffer

#define oslGetDrawBuffer

(

)

osl_curBuf

Returns the current drawbuffer as an OSL_IMAGE. You can save it to restore it later.

Returns

A pointer to the current drawbuffer image.

OSL_DEFAULT_BUFFER

#define OSL_DEFAULT_BUFFER   (&osl_defaultBufferImage)

An image representing the primary buffer image, which is the buffer to which you are currently writing.

Note

This buffer is managed by oslSwapBuffers. In single buffering mode, OSL_DEFAULT_BUFFER is identical to OSL_SECONDARY_BUFFER.

OSL_SECONDARY_BUFFER

#define OSL_SECONDARY_BUFFER   (&osl_secondaryBufferImage)

An image representing the secondary buffer image, which is the buffer currently displayed to the user.

Note

In single buffering mode, OSL_DEFAULT_BUFFER is identical to OSL_SECONDARY_BUFFER. This buffer is updated and managed by oslSwapBuffers.

OSL_SCREEN_WIDTH

#define OSL_SCREEN_WIDTH   (osl_curBuf->sizeX)

Returns the width of the current drawbuffer.

Returns

The width of the current drawbuffer in pixels. For the default drawbuffer (i.e., the screen), it will be 480 pixels, which is the resolution of the PSP LCD.

OSL_SCREEN_HEIGHT

#define OSL_SCREEN_HEIGHT   (osl_curBuf->sizeY)

Returns the height of the current drawbuffer.

Returns

The height of the current drawbuffer in pixels. For the default drawbuffer (i.e., the screen), it will be 272 pixels, which is the resolution of the PSP LCD.

Enumeration Type Documentation

OSL_FX_ALPHAWRITE

enum OSL_FX_ALPHAWRITE

Available effects for oslSetAlphaWrite.

Enumerator
OSL_FXAW_NONE	Does not write alpha.
OSL_FXAW_SET	Sets alpha to value1 if the alpha channel of the pixel is not equal to value2.

OSL_FX_ALPHATEST

enum OSL_FX_ALPHATEST

Alpha test comparison operators. Used with oslSetAlphaTest to define the conditions for alpha testing.

Enumerator
OSL_FXAT_NEVER	Never passes the alpha test.
OSL_FXAT_ALWAYS	Always passes the alpha test.
OSL_FXAT_EQUAL	Passes the alpha test if the alpha value is equal to the reference value.
OSL_FXAT_NOTEQUAL	Passes the alpha test if the alpha value is not equal to the reference value.
OSL_FXAT_LESS	Passes the alpha test if the alpha value is less than the reference value.
OSL_FXAT_LEQUAL	Passes the alpha test if the alpha value is less than or equal to the reference value.
OSL_FXAT_GREATER	Passes the alpha test if the alpha value is greater than the reference value.
OSL_FXAT_GEQUAL	Passes the alpha test if the alpha value is greater than or equal to the reference value.

Function Documentation

oslSetDrawBuffer()

void oslSetDrawBuffer ( OSL_IMAGE *  img )

extern

Define an image as the current drawbuffer. Use this function to specify the image to which drawing operations will be directed. Remember to restore the original drawbuffer after you have finished drawing.

OSL_IMAGE *drawBuf = oslCreateImage(320, 182, OSL_IN_VRAM, OSL_PF_5650);
// Clear the image to black
oslClearImage(drawBuf, RGB16(0, 0, 0));
// Set that image as the drawbuffer
oslSetDrawBuffer(drawBuf);
// Draw a red filled rectangle on the image
oslDrawFillRect(0, 0, 100, 100, RGB(255, 0, 0));
// Restore the default drawbuffer
oslSetDrawBuffer(OSL_DEFAULT_BUFFER);
// Draw that image somewhere on the screen
oslDrawImageXY(drawBuf, 80, 45);

Important:

• The image pixel format must be non-paletted. Supported formats are 4444, 5551, 5650, and 8888. Note that 8888 mode (32-bit) is slower and results in a larger image size.
• The image must be in video memory (OSL_IN_VRAM). The GPU can only render into video memory (it reads textures from both RAM and VRAM).
• A common issue is that the image may not be displayed if its alpha is null. To avoid this, either clear the image after creation or temporarily disable alpha blending by calling oslSetAlpha(OSL_FX_NONE, 0).

Parameters

img	The image to set as the current drawbuffer.

oslSetAlphaWrite()

void oslSetAlphaWrite ( int  action, int  value1, int  value2  )

extern

Controls writing to the alpha channel of the draw buffer.

This function is useful when rendering to an image rather than the standard draw buffer. By default, alpha values are not modified in the draw buffer. This function allows you to specify how alpha values should be written based on the given action. It also provides the ability to enable or disable stencil testing, which can control the regions of the buffer where alpha values are written.

Parameters

action	Specifies the action to take: OSL_FXAW_SET: Sets the alpha channel to value1. Every pixel written to the draw buffer will set its alpha value to value1. Even fully transparent pixels will have their alpha values set unless additional alpha testing is enabled. OSL_FXAW_NONE: Disables stencil testing, leaving the alpha channel unchanged.
value1	If action is OSL_FXAW_SET, this specifies the alpha value to be written, ranging from 0 (transparent) to 255 (opaque).
value2	Currently not used; should be set to 0.

Example:

// Clear the image to fully transparent (alpha = 0)
oslClearImage(buffer, RGBA(0, 0, 0, 0));
// Set the cleared image as the draw buffer
oslSetDrawBuffer(buffer);
// Enable alpha writing with full opacity (alpha = 255)
oslSetAlphaWrite(OSL_FXAW_SET, 255, 0);
// Only draw pixels with an alpha value greater than 0, preventing fully transparent pixels from being written
oslSetAlphaTest(OSL_FXAT_GREATER, 0);
// Continue rendering...

oslSetAlphaTest()

void oslSetAlphaTest ( int  condition, int  value  )

extern

Sets alpha testing parameters.

Configures the alpha test, which determines whether a pixel should be drawn based on its alpha value. If the test passes, the pixel is written to the screen; otherwise, it is ignored.

Parameters

condition

The condition for the test to pass. Can be one of the following: OSL_FXAT_NEVER: Never passes. OSL_FXAT_ALWAYS: Always passes. OSL_FXAT_EQUAL: Alpha is equal to the value. OSL_FXAT_NOTEQUAL: Alpha is not equal to the value. OSL_FXAT_LESS: Alpha is less than the value. OSL_FXAT_LEQUAL: Alpha is less than or equal to the value. OSL_FXAT_GREATER: Alpha is greater than the value. OSL_FXAT_GEQUAL: Alpha is greater than or equal to the value.

value

The reference value for comparison.

Note

Pixels from an OSL_PF_5650 image do not initially contain alpha. The alpha value is automatically set to opaque (alpha = 255).

oslDisableAlphaTest()

void oslDisableAlphaTest ( )

extern

Disables alpha testing.

Alpha testing is a method of controlling the visibility of pixels based on their alpha values.

Variable Documentation

osl_alphaTestEnabled

int osl_alphaTestEnabled

extern

Holds whether alpha testing is currently enabled.