问题
I'm loading textures using OpenGL ES, the below is my code.
The graphic is made up of 2 textures of the same size, the stop button and the blue glow behind.
The first graphic below was taken using the iPad simulator in xCode, and the 2nd on the actual device. The 1st graphic is the correct output as I exported the graphics from Illustrator. However, when I loaded the program on the iPad, it gives me the 2nd graphic. It seems somehow that the blue light texture behind the stop button has become smaller. Why is this so?
I can compensate by making the blue light texture bigger, but it wouldn't be right as the way it is supposed to look in Illustrator is the 1st graphic.
Here's my code.
//
// OpenGLES_Ch3_4ViewController.m
// OpenGLES_Ch3_4
//
#import "OpenGLES_Ch3_4ViewController.h"
#import "AGLKVertexAttribArrayBuffer.h"
#import "AGLKContext.h"
#define Y_POS 1.0
#define ASPECT_RATIO 0.75f
#define SIZE 0.8
@implementation OpenGLES_Ch3_4ViewController
@synthesize baseEffect;
@synthesize vertexBuffer;
@synthesize textureInfo0;
@synthesize textureInfo1;
/////////////////////////////////////////////////////////////////
// This data type is used to store information for each vertex
typedef struct {
GLKVector3 positionCoords;
GLKVector2 textureCoords;
}
SceneVertex;
/////////////////////////////////////////////////////////////////
// Define vertex data for a triangle to use in example
//static const SceneVertex vertices[] =
static const SceneVertex vertices[] =
{
{{-1.0f*SIZE, -ASPECT_RATIO*SIZE, 0.0f}, {0.0f, 0.0f}}, // first triangle
{{ 0.0f*SIZE, -ASPECT_RATIO*SIZE, 0.0f}, {1.0f, 0.0f}},
{{-1.0f*SIZE, 0.0f*SIZE, 0.0f}, {0.0f, 1.0f}},
{{ 0.0f*SIZE, -ASPECT_RATIO*SIZE, 0.0f}, {1.0f, 0.0f}}, // second triangle
{{-1.0f*SIZE, 0.0f*SIZE, 0.0f}, {0.0f, 1.0f}},
{{ 0.0f*SIZE, 0.0f*SIZE, 0.0f}, {1.0f, 1.0f}},
};
/////////////////////////////////////////////////////////////////
// Called when the view controller's view is loaded
// Perform initialization before the view is asked to draw
- (void)viewDidLoad
{
[super viewDidLoad];
// Verify the type of view created automatically by the
// Interface Builder storyboard
GLKView *view = (GLKView *)self.view;
NSAssert([view isKindOfClass:[GLKView class]],
@"View controller's view is not a GLKView");
// Create an OpenGL ES 2.0 context and provide it to the
// view
view.context = [[AGLKContext alloc]
initWithAPI:kEAGLRenderingAPIOpenGLES2];
// Make the new context current
[AGLKContext setCurrentContext:view.context];
// Create a base effect that provides standard OpenGL ES 2.0
// shading language programs and set constants to be used for
// all subsequent rendering
self.baseEffect = [[GLKBaseEffect alloc] init];
self.baseEffect.useConstantColor = GL_TRUE;
self.baseEffect.constantColor = GLKVector4Make(
1.0f, // Red
1.0f, // Green
1.0f, // Blue
1.0f);// Alpha
// Set the background color stored in the current context
((AGLKContext *)view.context).clearColor = GLKVector4Make(
0.0f, // Red
0.0f, // Green
0.0f, // Blue
1.0f);// Alpha
// Create vertex buffer containing vertices to draw
self.vertexBuffer = [[AGLKVertexAttribArrayBuffer alloc]
initWithAttribStride:sizeof(SceneVertex)
numberOfVertices:sizeof(vertices) / sizeof(SceneVertex)
bytes:vertices
usage:GL_STATIC_DRAW];
// Setup texture0
CGImageRef imageRef0 =
[[UIImage imageNamed:@"stoplight_full.png"] CGImage];
self.textureInfo0 = [GLKTextureLoader
textureWithCGImage:imageRef0
options:[NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES],
GLKTextureLoaderOriginBottomLeft, nil]
error:NULL];
self.textureInfo0_2 = [GLKTextureLoader
textureWithCGImage:imageRef0
options:nil
error:NULL];
// Setup texture1
CGImageRef imageRef1 =
[[UIImage imageNamed:@"stop_button.png"] CGImage];
self.textureInfo1 = [GLKTextureLoader
textureWithCGImage:imageRef1
options:[NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES],
GLKTextureLoaderOriginBottomLeft, nil]
error:NULL];
self.textureInfo1_2 = [GLKTextureLoader
textureWithCGImage:imageRef1
options:nil
error:NULL];
// Enable fragment blending with Frame Buffer contents
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
}
/////////////////////////////////////////////////////////////////
// GLKView delegate method: Called by the view controller's view
// whenever Cocoa Touch asks the view controller's view to
// draw itself. (In this case, render into a frame buffer that
// shares memory with a Core Animation Layer)
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
// Clear back frame buffer (erase previous drawing)
[(AGLKContext *)view.context clear:GL_COLOR_BUFFER_BIT];
[self.vertexBuffer prepareToDrawWithAttrib:GLKVertexAttribPosition
numberOfCoordinates:3
attribOffset:offsetof(SceneVertex, positionCoords)
shouldEnable:YES];
[self.vertexBuffer prepareToDrawWithAttrib:GLKVertexAttribTexCoord0
numberOfCoordinates:2
attribOffset:offsetof(SceneVertex, textureCoords)
shouldEnable:YES];
self.baseEffect.texture2d0.name = self.textureInfo0.name;
self.baseEffect.texture2d0.target = self.textureInfo0.target;
[self.baseEffect prepareToDraw];
// Draw triangles using the vertices in the
// currently bound vertex buffer
[self.vertexBuffer drawArrayWithMode:GL_TRIANGLES
startVertexIndex:0
numberOfVertices:sizeof(vertices) / sizeof(SceneVertex)];
self.baseEffect.texture2d0.name = self.textureInfo1.name;
self.baseEffect.texture2d0.target = self.textureInfo1.target;
[self.baseEffect prepareToDraw];
// Draw triangles using currently bound vertex buffer
[self.vertexBuffer drawArrayWithMode:GL_TRIANGLES
startVertexIndex:0
numberOfVertices:sizeof(vertices) / sizeof(SceneVertex)];
}
回答1:
To me, the second texture does not look smaller, just dimmer. Your laptop and iPad most likely have displays with different gammas.
There are many ways to correct for gamma, a terrific introduction is provided here.
It is worth noting many modern cards can do it for you these days too, but so far unsupported on OpenGL ES as far as I know: sRGB Color Formats.
来源：https://stackoverflow.com/questions/14493142/ios-opengl-es-different-texture-behaviour-on-simulator-and-device